func_code_string: #include <bits/stdc++.h>   using namespace std;   const long long N = 2e5 + 5, inf = 1e9 + 7;   long long n, k;   string s, t;   signed main() {     ios_base::sync_with_stdio(false);     cin.tie(0);     long long i, j, a, b, ans = 0;     cin >> n >> k >> s >> t;     ans = n;     i = 0;     while (i < n && s[i] == t[i]) i++;     long long t1 = 0, t2 = 0, a1 = 1, a2 = 1;     k--;     if (i < n && k) {       ans += n - i;       k--;       i++;     }     for (; i < n; i++) {       if (s[i] ==  a ) {         ans += min(k, t1 + 1) * (n - i);         k -= min(k, t1 + 1);         t1 = t1 * 2 + 1;       } else {         ans += min(k, t1) * (n - i);         k -= min(k, t1);         t1 *= 2;       }       if (t[i] ==  a ) {         ans += min(k, t2) * (n - i);         k -= min(k, t2);         t2 *= 2;       } else {         ans += min(k, t2 + 1) * (n - i);         k -= min(k, t2 + 1);         t2 = t2 * 2 + 1;       }       if (!k) break;     }     cout << ans;   }   