func_code_string: #include <bits/stdc++.h>   using namespace std;   char s[1000001], t[1000001];   long long z[1000001], c[1000001];   int main() {     int n, k;     scanf( %d%d%s%s , &n, &k, s + 1, t + 1);     if (k == 1) {       printf( %d n , k * n);       return 0;     }     int o = 1;     while (o <= n && s[o] == t[o]) o++;     if (o > n) {       printf( %d n , n);       return 0;     }     long long ans = n + (n - o + 1);     k -= 2;     o++;     while (o <= n) {       if (s[o] ==  a ) z[n - o + 1]++;       if (t[o] ==  b ) z[n - o + 1]++;       o++;     }     for (int i = n; i; i--) {       z[i] += c[i];       c[i - 1] += c[i];       int kk = min(1ll * k, z[i]);       ans += 1ll * i * kk;       k -= kk;       c[i - 1] += kk;     }     printf( %I64d n , ans);   }   