package yukicoder;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class yukicoder015 {
	public static void main(String[] args){
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String tes = null;
		
		try {
			tes = br.readLine();
			} catch (IOException e) {
				// TODO 自動生成された catch ブロック
				e.printStackTrace();
		}
		
		String[] sp = tes.split(" ");
		
		int n = Integer.parseInt(sp[0]);
		int k = Integer.parseInt(sp[1]);
		
		
		try {
			tes = br.readLine();
			} catch (IOException e) {
				// TODO 自動生成された catch ブロック
				e.printStackTrace();
		}
		
		aisu soft = new aisu(tes);
		
		String lol = tes;
		char tmp;
		int countka = 0;
		for(int i=0;i<k;i++){
			tmp = soft.eat();
			if(tmp == '1'){
				if(k <= soft.getKazu()){
					break;
				}
				kkk(soft,1,k);
			}else if(tmp == '2'){
				if(k <= soft.getKazu()){
					break;
				}
				kkk(soft,2,k);
			}
			
			countka++;
			if(k <= soft.getKazu()){
				break;
			}
		}
		
		System.out.println(countka);
		
		
		
	}
	private static void kkk(aisu soft, int tugi,int k) {
		int tmp;
		for(int i=0;i<tugi;i++){
			tmp = soft.eat();
			if(tmp == '1'){
				if(k <= soft.getKazu()){
					return;
				}
				kkk(soft,1,k);
			}else if(tmp == '2'){
				if(k <= soft.getKazu()){
					return;
				}
				kkk(soft,2,k);
			}
		}
	}
}
class aisu{
	private String hako;
	private int basyo =0;
	private int max;
	
	
	private int kazu = 0;
	
	public aisu(String tmp){
		hako = tmp;
		max = hako.length();
	}
	
	public char eat(){
		char ret;
		
		ret = hako.charAt(basyo);
		ink();
		kazu++;
		return ret;
	}
	
	private void ink(){
		basyo++;
		basyo = basyo % max;
	}
	
	public String getHako() {
		return hako;
	}
	public int getBasyo() {
		return basyo;
	}

	public int getMax() {
		return max;
	}

	public int getKazu() {
		return kazu;
	}
	
	
}