func_code_string: #include <bits/stdc++.h>   using namespace std;   const int P = 1e9 + 7, INF = 0x3f3f3f3f;   long long gcd(long long a, long long b) { return b ? gcd(b, a % b) : a; }   long long qpow(long long a, long long n) {     long long r = 1 % P;     for (a %= P; n; a = a * a % P, n >>= 1)       if (n & 1) r = r * a % P;     return r;   }   long long inv(long long first) {     return first <= 1 ? 1 : inv(P % first) * (P - P / first) % P;   }   inline int rd() {     int first = 0;     char p = getchar();     while (p <  0  || p >  9 ) p = getchar();     while (p >=  0  && p <=  9 ) first = first * 10 + p -  0 , p = getchar();     return first;   }   const int N = 1e6 + 10;   int n;   long long k;   char s[N], t[N];   int main() {     scanf( %d%lld%s%s , &n, &k, s + 1, t + 1);     long long ans = 0, tot = 1, INF = 1e15;     for (int i = 1; i <= n; ++i) {       tot <<= 1;       if (s[i] ==  b ) --tot;       if (t[i] ==  a ) --tot;       ans += min(k, tot);       tot = min(tot, INF);     }     printf( %lld n , ans);   }   