spoj_pt07z.cpp

#include <bits/stdc++.h>

#define ll long long

#define ld long double

#define endl '\n'

#define vll vector<ll>

#define vvll vector< vll >

#define Cout(x)        cout << #x << " " << x << endl

#define pll pair<ll ,ll >

#define vpll vector< pll >

#define mp make_pair

#define pb push_back

#define MOD 1000000007

#define inf 1e18;

#define vfind(v,x) (find(all(v),x) != (v).end())

#define clr(c) (c).clear()

#define cres(c,n) (c).clear(),(c).resize(n)

#define ios ios_base::sync_with_stdio(false);cin.tie(NULL);cout.tie(NULL)

#define all(v) v.begin(),v.end()

#define rall(v) v.rbegin(),v.rend()

#define fst first

#define scd second

#define eb(a) emplace_back(a)

#define ef(a) emplace_front(a)

#define fr(i,n) for(ll (i) = 0 ; (i) < (n) ; ++(i))

#define fr1(i,n) for(ll (i) = 1 ; (i) <= (n) ; ++(i))

#define frr(i,n) for(ll (i) = (n)-1 ; (i)>=0 ; --(i))

#define frab(i,a,b,c) for(ll (i) = a ; (i) <= (b) ; (i)+=(c))



#define mst(A) memset( (A) , 0 , sizeof(A) );


using namespace std;


void write(vll &oneD){

	for(ll i=0;i<oneD.size();i++){

		printf("%lld ",oneD[i]);

	}

	printf("\n");

}

void write(vvll &twoD){

	for(ll i=0;i<twoD.size();i++){

		write(twoD[i]);

	}

}

void write(vpll &oneDP){

	fr(i,oneDP.size()){

		printf("%lld %lld\n" , oneDP[i].fst , oneDP[i].scd);

	}
	cout<<"\n";

}

void write(map< ll , ll > &mpp){

	for(map<ll , ll >::iterator it = mpp.begin() ; it != mpp.end() ; it++){

		cout<<it->fst<<" : "<<it->scd<<endl;

	}

	cout<<endl;

}
bool cmp(const pair<ll,ll> &a,const pair<ll,ll> &b)
{
    if(a.first == b.first)
        return (a.scd >= b.scd);

    return (a.first < b.first);
}


vll seive;
vll primes;

void Seive(){

	const ll maxn = 100005;

	seive.resize(maxn);
	fr(i,maxn) seive[i] = 1;

	for(ll i=2;i*i<maxn;i++)
	{
	     if(seive[i]==1 )
            {
                for(ll j = i*i ; j <maxn ; j+=i)
                {
                         seive[j] = 0;
                }
            }
    }
	primes.pb(2);
	for(ll i=3;i<maxn;i+=2)
    {
        if(seive[i])
            primes.pb(i);
    }
}


ll isprime(ll N){
    if(N<2 || (!(N&1) && N!=2))
        return 0;
    for(ll i=3; i*i<=N; i+=2){
        if(!(N%i))
            return 0;
    }
    return 1;
}


ll power(ll x, ll y , ll m){

    long long int res = 1;

    x = x % m;

    while (y > 0)
    {
        // If y is odd, multiply x with result
        if (y & 1)
            res =(res*x)%MOD;

        // y must be even now
        y = y>>1; // y = y/2
        x = (x*x)%MOD;
    }
    return res;
}


ll modinv(ll x , ll mod = MOD){

	return power(x , mod - 2 , mod);

}
////////////////////////////////////////////////////////////////////////////////


ll A[10005];
ll B[1001];
ll dis[10005];
ll visited[10005];
vll v[10050];
   ll mx=0,my=0;
   ll n;
   void init(ll n)
   {
       fr1(i,n)
       {
           dis[i]=0;
           visited[i]=0;
       }
   }
ll dfs(ll x)
{
    visited[x]=1;

    for(int it : v[x])
    {
        if(!visited[it])
        {
            dis[it]=1+dis[x];
            if(dis[it] > mx)
            {
                 mx=max(dis[it],mx);
                 my=it;
                 dis[it]=mx;
                  //cout<<mx<<" "<<my<<endl;
            }
            visited[it]=1;

            dfs(it);
        }
    }

    fr1(i,n)
    {
        if(dis[i]==mx)
        {
            my=i;
        }
    }

    //cout<<my<<endl;

    return my;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    #ifndef ONLINE_JUDGE
    freopen("allo.txt","r",stdin);
    #endif
      //  freopen("out.txt","w",stdout);




    ll a,b,c,d;
    ll k,l,m,p,q,r,t,x,y;

        //cin>>t;while(t--){    map<ll,ll> M; string s;


        cin>>n;
        if(n==1)
        {
            cout<<0<<endl;
            return 0;
        }
        fr(i,n-1)
        {

            cin>>a>>b;
            v[a].pb(b);
            v[b].pb(a);
            //cout<<A[i];
        }
        dis[1]=0;
        p=dfs(1);
    init(n);
    dis[p]=0;
        p=dfs(p);
       // Cout(p);
        cout<<dis[p]<<endl;


        //   }




}