using System;
using System.Linq;

public class MyClass
{
    public static void Main()
    {
        var array = Array.ConvertAll<string, int>(Console.ReadLine().Split(new char[] { ' ' }, StringSplitOptions.RemoveEmptyEntries), int.Parse);
        int N = array[0];
        long K = array[1];
        var str = Console.ReadLine();
        long res = 0;
        int cnt = 0;
        for (int i = 0; i <=N&&K>0; i++)
        {
            res += Count(str, (int)Math.Min(K, N), ref cnt);
            K -= Math.Min(K, N);
        }//for i
        long increase = Count(str, N, ref cnt);
        res += K / N * increase;
        K-=N*increase;
        res += Count(str, (int)K, ref cnt);
        Console.WriteLine(res);
    }

    private static long Count(string str, int need,ref int cnt)
    {
        int res = 0;
        for (int i = 0; i < need; i++)
        {
            cnt--;
            if (cnt < 0)
            {
                res++;
                cnt++;
            }//if
            cnt += str[i] - '0';
        }//for i
        return res;
    }

}