func_code_string: #include <bits/stdc++.h>   using namespace std;   char s[500005], t[500005];   long long ans;   int n, k, now, tmp;   int main() {     scanf( %d %d n , &n, &k);     fread(s + 1, 1, n, stdin);     getchar();     fread(t + 1, 1, n, stdin);     s[n + 1] =  # ;     if (k == 1) return printf( %d n , n), 0;     for (now = 1; s[now] == t[now]; now++)       ;     if (now > n) return printf( %d n , n), 0;     ans = now + 1;     for (int i = now + 1; i <= n; i++) {       tmp = tmp << 1;       if (s[i] ==  a ) tmp++;       if (t[i] ==  b ) tmp++;       tmp = min(k - 2, tmp);       ans += tmp + 2;     }     printf( %lld n , ans);   }   