func_code_string: #include <bits/stdc++.h>   using namespace std;   template <typename Arg1>   void ZZ(const char* name, Arg1&& arg1) {     std::cerr << name <<   =   << arg1 << endl;   }   template <typename Arg1, typename... Args>   void ZZ(const char* names, Arg1&& arg1, Args&&... args) {     const char* comma = strchr(names + 1,  , );     std::cerr.write(names, comma - names) <<   =   << arg1;     ZZ(comma, args...);   }   int n, u, v;   int nxt[1000010], ans[1000010], cnt[1000010];   pair<int, int> a[1000000];   signed main() {     ios_base::sync_with_stdio(0);     cin.tie(0);     ;     cin >> n;     for (int i = 0; i < n; i++) {       cin >> a[i].first >> a[i].second;       cnt[a[i].second] = 1;       nxt[a[i].first] = a[i].second;       if (!a[i].first) u = a[i].second;     }     for (int i = 0; i < n; i++) {       if (!cnt[a[i].first]) {         v = a[i].first;         break;       }     }     for (int i = 0; i < n; i += 2) {       ans[i] = v;       v = nxt[v];     }     for (int i = 1; i < n; i += 2) {       ans[i] = u;       u = nxt[u];     }     for (int i = 0; i < n; i++) cout << ans[i] <<    ;     return 0;   }   