#include <bits/stdc++.h>
using namespace std;
using ll=long long;
int main(){
	int n;
	cin>>n;
	ll a;
	cin>>a;
	string s;
	cin>>s;
	ll x=0,y=0,z=0;
	for(int i=0;i<n;i++){
		if(s[i]=='0')x++;
		else{
			if(x!=0){
				a--;
				x--;
				z++;
				if(a==0){
					cout<<i+1<<endl;
					return 0;
				}
			}else y++;
		}
	}
		
	ll cnt=z;
	ll ans=n;
	ll xx=x;
	if(x==0){
		ans+=n*((a-1)/cnt);
		a=(a-1)%cnt+1;
		for(int i=0;i<n;i++){
			if(s[i]=='0')x++;
			else{
				if(x!=0){
					a--;
					x--;
					if(a==0){
						cout<<ans+i+1<<endl;
						return 0;
					}
				}
			}
		}
		assert(0);
	}else if(x>=y){
		z+=y;
		ans+=n*((a-1)/z);
		a=(a-1)%z+1;
		for(int i=0;i<n;i++){
			if(s[i]=='0')x++;
			else{
				if(x!=0){
					a--;
					x--;
					if(a==0){
						cout<<ans+i+1<<endl;
						return 0;
					}
				}
			}
		}
		assert(0);
	}else{
		z+=x;
		ans+=n*((a-1)/z);
		a=(a-1)%z+1;

		for(int i=0;i<n;i++){
			if(s[i]=='0')x++;
			else{
				if(x!=0){
					a--;
					x--;
					if(a==0){
						cout<<ans+i+1<<endl;
						return 0;
					}
				}
			}
		}
		assert(0);
	}
}