func_code_string: #include <bits/stdc++.h>   using namespace std;   inline long long read() {     long long f = 1, x = 0;     char ch = getchar();     while (ch <  0  || ch >  9 ) {       if (ch ==  - ) f = -1;       ch = getchar();     }     while (ch >=  0  && ch <=  9 ) {       x = x * 10 + ch -  0 ;       ch = getchar();     }     return x * f;   }   const int maxn = 5e5 + 5;   char st1[maxn], st2[maxn];   long long ans = 0, pre = 0;   int n, k;   int main() {     n = read(), k = read();     scanf( %s , st1);     scanf( %s , st2);     for (int i = 0; i <= n - 1; i++) {       pre = min(pre * 2 + (int)(st2[i] - st1[i]), 1ll << 36);       ans += min(pre + 1, (long long)k);     }     cout << ans << endl;     return 0;   }   