#include <bits/stdc++.h>   using namespace std;   void ga(int N, int *A) {     for (int i(0); i < N; i++) scanf( %d , A + i);   }   char s[222222], r[222222];   int N, A, B;   int main(void) {     scanf( %s%s , s, r), N = strlen(s);     for (int i(0); i < N; i++)       if (s[i] ^ r[i]) A += s[i] == 52, B += s[i] != 52;     printf( %d n , max(A, B));     return 0;   }   