#include <bits/stdc++.h>   using namespace std;   int main() {     char c[100005];     scanf( %s , c);     vector<char> v;     int count[26];     int instk[26];     memset(count, 0, sizeof(count));     memset(instk, 0, sizeof(instk));     int find = 0;     for (int i = 0; c[i] != 0; i++) count[c[i] -  a ]++;     while (count[find] == 0) find++;     for (int i = 0; c[i] != 0; i++) {       v.push_back(c[i]);       count[c[i] -  a ]--;       while (count[find] == 0) find++;       while (!v.empty() && v.back() -  a  <= find) {         printf( %c , v.back());         v.pop_back();       }     }     while (!v.empty()) {       printf( %c , v.back());       v.pop_back();     }   }   