#include <iostream>

int main()
{
    int n, k;
    std::cin >> n >> k;
    
    char s[n + 1];
    std::cin >> s;
    
    int win = 0;
    int eat = 0;
    int buy = 0;
    
    int p = 0;
    
    while(eat < k)
    {
        if(win)
            win--;
        else
            buy++;
        
        eat++;
        
        win += s[p] - '0';
        
        p++;
        p %= n;
    }
    
    std::cout << buy << std::endl;
    
    return 0;
}