CF1083B The Fair Nut and Strings

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 typedef long long ll;
 4 int main()
 5 {
 6     int n, k; string a, b;
 7     while (cin >> n >> k >> a >> b)
 8     {
 9         ll ans = 0, cur = 1;
10         for (int i = 0; i < n; i++)
11         {
12             cur <<= 1;
13             if (a[i] == ‘b‘) cur--;
14             if (b[i] == ‘a‘) cur--;
15             if (cur >= k)
16             {
17                 ans += ((ll)n - i) * k;
18                 break;
19             }
20             ans += cur;
21         }
22         cout << ans << endl;
23     }
24     return 0;
25 }