#define _USE_MATH_DEFINES

#include <iostream>
#include <iomanip>

#include <algorithm>
#include <cmath>

#include <string>
#include <list>
#include <queue>
#include <vector>
#include <complex>
#include <set>

/////////
#define REP(i, x, n) for(int i = x; i < n; i++)
#define rep(i,n) REP(i,0,n)
#define P(p) cout<<(p)<<endl;
/////////
typedef long long LL;
typedef long double LD;
/////////
using namespace::std;
/////////

int main(void){
    std::cin.tie(0); 
    std::ios::sync_with_stdio(false);
    std::cout << std::fixed;//
    //cout << setprecision(6);//

	int N,K;
	string str;
	cin>>N>>K>>str;

	int Limit=0,ama=0;//１箱を買い切る本数、１箱を越える余り当たり
	int sum=0;//現在までの取得本数
	int kpn = K%N;
	int kpnB = 0;
	bool buy = false;//購入フラグ
	int count = 0;//購入本数
	for(int i=0;i < N;++i){
		if( i+1 > sum){
			++sum;
			++Limit;
			buy = true;
		}else{buy = false;}
		sum += str[i] - '0';
		if(buy == true){++count;}
		if( kpn != 0 && sum >= kpn && kpnB == 0){
			kpnB = count;
		}
	}
	if(N!=1){
		ama = sum%N;
	}else{
		ama = sum - 1;
	}

	if( Limit <= ama ){
		if(K<N){
			P(kpnB);
		}else{
			P(Limit);
		}
	}else if( ama <= 0 ){
		P( K/N * Limit + kpnB );
	}else{
		int ans = 0;
		int nokori ;
		int kuriAma = 0;
		if( K >= 2*N ){
			ans += Limit + (Limit-ama)*(K/N-2);//買う
			//N*(S-1)+ama取得_?
			nokori = N + kpnB; 
			kuriAma = ama;
		}else{
			nokori  = K;
			kuriAma = 0;
		}
		int sum2 = kuriAma;
		int count2 = 0;
		for(int i=0; i<2*N;++i){
			if( i+1 > sum2){
				++sum2;
				++count2;
			}
			sum2 += str[i%N] - '0';
			if( sum2 >= nokori ){
				break;
			}
		}
		P(ans + count2);
	}
    return 0;
}