func_code_string: #include <bits/stdc++.h>   using namespace std;   int main() {     long long n, i, tmp_ara1, tmp_ara2;     vector<long long> ara1(2000007, -1), ara2(2000007, -1), ans(200007, -1),         in_front;     cin >> n;     for (i = 1; i <= n; i++) {       cin >> tmp_ara1 >> tmp_ara2;       ara1[tmp_ara1] = tmp_ara2;       ara2[tmp_ara2] = tmp_ara1;       in_front.push_back(tmp_ara1);     }     long long key = 0;     for (i = 2; i <= n; i += 2) {       ans[i] = ara1[key];       key = ara1[key];     }     long long first;     for (i = 0; i < n; i++) {       if (ara2[in_front[i]] == -1) {         first = in_front[i];         break;       }     }     key = first;     ans[1] = first;     for (i = 3; i <= n; i += 2) {       ans[i] = ara1[key];       key = ara1[key];     }     for (i = 1; i <= n; i++) {       cout << ans[i] <<    ;     }     return 0;   }   