#include <bits/stdc++.h>   long int temp, i, j, k, T;   long int ABS(int test) {     if (test < 0)       return test * -1;     else       return test;   }   int x8[] = {1, 1, 0, -1, -1, -1, 0, 1};   int y8[] = {0, 1, 1, 1, 0, -1, -1, -1};   int x4[] = {1, 0, -1, 0};   int y4[] = {0, 1, 0, -1};   long int arr[1000000];   long int buff[1000000];   long int memo[1000000];   using namespace std;   int main() {     char a[100001];     char b[100001];     int jawaban = 0, panjang, tujuh1 = 0, tujuh2 = 0, empat1 = 0, empat2 = 0;     memset(memo, 0, sizeof memo);     cin >> a;     cin >> b;     panjang = strlen(a);     for (i = 0; i < panjang; i++) {       if (a[i] ==  7 ) tujuh1++;       if (a[i] ==  4 ) empat1++;       if (b[i] ==  7 ) tujuh2++;       if (b[i] ==  4 ) empat2++;     }     for (i = 0; i < panjang; i++) {       if (a[i] == b[i]) {         if (a[i] ==  7 ) {           tujuh1--;           tujuh2--;         }         if (a[i] ==  4 ) {           empat1--;           empat2--;         }       }     }     jawaban = max(tujuh1, tujuh2);     cout << jawaban << endl;     {       fflush(stdin);       getchar();     };     return 0;   }   