import java.math.BigDecimal;
import java.util.Arrays;
import java.util.Scanner;

public class Main {
	
	public static long simulate(final int N, int[] S, long K, final long initial_bonus){
		long bonus = initial_bonus;
		long cost = 0;
		
		for(long i = 0; i < K; i++){
			final int index = (int)(i % N);
			
			if(bonus > 0){
				bonus--;
			}else{
				cost++;
			}
			
			bonus += S[index];
		}
		
		return cost;
	}
	
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		
		final int N = sc.nextInt();
		final long K = sc.nextLong();
		
		char[] inputs = sc.next().toCharArray();
		int[] S = new int[N];
		for(int i = 0; i < N; i++){ S[i] = Character.getNumericValue(inputs[i]); }
		
		int one_cycle_cost = 0, one_cycle_bonus = 0;
		for(int i = 0; i < N; i++){
			if(one_cycle_bonus > 0){
				one_cycle_bonus--;
			}else{
				one_cycle_cost++;
			}
			
			one_cycle_bonus += S[i];
		}
		
		if(one_cycle_bonus > 0){
			if(one_cycle_bonus >= one_cycle_cost){
				System.out.println(one_cycle_cost);
			}else{
				System.out.println(one_cycle_cost + Math.max(0, one_cycle_cost - one_cycle_bonus) * Math.max(0, K / N - 1) + simulate(N, S, K % N, one_cycle_bonus));
			}
			
		}else{
			System.out.println((K / N * one_cycle_cost) + simulate(N, S, K % N, 0));
		}	
	}
}