func_code_string: #include <bits/stdc++.h>   using namespace std;   const int N = 500005;   int n, k;   char a[N], b[N];   int main() {     scanf( %d%d%s%s , &n, &k, a, b);     long long cur = 1, ans = 0;     if (k == 1) {       cout << n << endl;       return 0;     }     for (int i = 0; i < n; i++) {       cur *= 2;       if (a[i] !=  a ) --cur;       if (b[i] !=  b ) --cur;       cur = min(cur, k * 1ll);       ans += cur;     }     cout << ans << endl;     return 0;   }   