import java.io.*;
import java.util.StringTokenizer;

class Main{

static final PrintWriter out=new PrintWriter(System.out);
static int cnt;

public static void main(String[] args) throws IOException{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
String line="";
while((line=br.readLine())!=null&&!line.isEmpty()){
StringTokenizer st= new StringTokenizer(line);
int n=Integer.parseInt(st.nextToken());
int k=Integer.parseInt(st.nextToken());
int[] ice=new int[n];
line=br.readLine();
int hitiol=0;
int hit=0;
long ans=0;
long cnt=0;
for(int i=0;i<n;i++){
ice[i]=line.charAt(i)-'0';
hitiol+=ice[i];
}
if(k<n){
for(int i=0;i<k;i++){
hit--;
if(hit<0){
ans++;
hit++;
}
hit+=ice[i];
}
out.println(ans);
}
else{
for(int i=0;i<n;i++){
hit--;
if(hit<0){
ans++;
hit++;
}
hit+=ice[i];
}
if(hitiol>=n){
out.println(ans);
}
else{
int loop=(int)k/n-1;
ans+=hitiol*loop;
int rest=k%n;
for(int i=0;i<rest;i++){
hit--;
if(hit<0){
ans++; hit++;
}
hit+=ice[i];
}
out.println(ans);
}
}
out.flush();
}
}
}