213D.cpp

#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using str = string;
using pint = pair<int, int>;
using pll = pair<ll, ll>;
template<class T>using vc = vector<T>;
template<class T>using vvc = vc<vc<T>>;
using vint = vc<int>;
using vll = vc<ll>;
using vstr = vc<str>;
using vpint = vc<pint>;
using vpll = vc<pll>;
using vbool = vc<bool>;
using vvint = vvc<int>;
using vvll = vvc<ll>;

#define overload4(_1, _2, _3, _4, name, ...) name
#define rep1(n)          for(ll i = 0; i < (n); ++i)
#define rep2(i, n)       for(ll i = 0; i < (n); ++i)
#define rep3(i, a, b)    for(ll i = (a); i < (b); ++i)
#define rep4(i, a, b, c) for(ll i = (a); i < (b); i += (c))
#define rep(...) overload4(__VA_ARGS__, rep4, rep3, rep2, rep1)(__VA_ARGS__)
#define each1(a)       for(auto&& i : a)
#define each2(i,a)     for(auto&& i : a)
#define each3(x,y,a)   for(auto&& [x, y] : a)
#define each4(x,y,z,a) for(auto&& [x, y, z] : a)
#define each(...) overload4(__VA_ARGS__, each4, each3, each2, each1)(__VA_ARGS__)
#define all(x) (x).begin(), (x).end()

void yesno(bool flag){cout << (flag ? "Yes" : "No") << endl;}

vvll g; ll n;

void dfs(ll now, ll pre){
    cout << now << " ";
    each(i, g[now]){
        if(i == pre) continue;
        dfs(i, now);
        cout << now << " ";
    }
}

int main() {
    cin >> n;
    g.resize(n+1);
    rep(n-1){
        ll a, b; cin >> a >> b;
        g[a].push_back(b);
        g[b].push_back(a);
    }
    rep(i, 1, n+1) sort(all(g[i]));
    dfs(1, -1);
    cout << endl;
}