using System;
using System.Collections;
using System.Collections.Generic;
 
class TEST{
	static void Main(){
		Sol mySol =new Sol();
		mySol.Solve();
	}
}

class Sol{
	public void Solve(){
		
		int cnt=0;
		int stk=0;
		int p=0;
		while(K>0){
			if(p==N)p=0;
			if(stk>0){
				stk--;
			}else{
				cnt++;
			}
			K--;
			stk+=(int)(S[p]-'0');
			p++;
		}
		Console.WriteLine(cnt);
	}
	int N,K;
	String S;
	public Sol(){
		var d=ria();
		N=d[0];K=d[1];
		S=rs();
	}




	static String rs(){return Console.ReadLine();}
	static int ri(){return int.Parse(Console.ReadLine());}
	static long rl(){return long.Parse(Console.ReadLine());}
	static double rd(){return double.Parse(Console.ReadLine());}
	static String[] rsa(){return Console.ReadLine().Split(' ');}
	static int[] ria(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>int.Parse(e));}
	static long[] rla(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>long.Parse(e));}
	static double[] rda(){return Array.ConvertAll(Console.ReadLine().Split(' '),e=>double.Parse(e));}
}