char box[60];
n,k,x,y;
void hakogai(){
	int stock=0,cost=0,i;
	for(i=0;i<n;i++){
		if(stock>0)stock--;else cost++;
		stock+=box[i]-'0';
	}
	x=cost;
	y=stock;
}
int hasuu(int rest,int stock){
	int cost=0,i;
	for(i=0;i<rest;i++){
		if(stock>0)stock--;else cost++;
		stock+=box[i]-'0';
	}
	return cost;
}
int main(){
	scanf("%d%d%s",&n,&k,box);
	if(k<n)printf("%d",hasuu(k,0));
	else {
		hakogai();
		if(x<=y)printf("%d",x);
		else printf("%d",x+(x-y)*(k/n-1)+hasuu(k%n,y));
	}
	return 0;
}