#include "bits/stdc++.h"
#define REP(i,n,N) for(ll i=(n); i<(N); i++)
#define RREP(i,n,N) for(ll i=(N-1); i>=n; i--)
#define CK(n,a,b) ((a)<=(n)&&(n)<(b))
#define ALL(v) (v).begin(),(v).end()
#define p(s) cout<<(s)<<endl
#define p2(a,b) cout<<(a)<<" "<<(b)<<endl
#define v2(T) vector<vector<T>>
typedef long long ll;
using namespace std;
const ll mod= 1e9+7;

int dp[110];
int main(){
    int N,K;
    string s;
    cin>>N>>K;
    cin>>s;
    int cnt=s[0]-'0';

    dp[0]=1;
    REP(i,1,N){
        if(cnt>0){
            cnt--;
            dp[i] = dp[i-1];
        }else{
            dp[i] = dp[i-1]+1;
        }
        cnt+=s[i]-'0';
    }
    int ans = dp[min(K,N)-1];
    if(K<=N){
        p(ans);
        return 0;
    }
    K-=N;
    dp[N-1]=0;
    REP(i,0,N){
        if(cnt>0){
            cnt--;
            dp[i]=dp[(i-1+N)%N];
        }else{
            dp[i]=dp[(i-1+N)%N]+1;
        }
        cnt+=s[i]-'0';
    }
    ans+=dp[N-1]*(K/N);
    if(K%N>0)ans+=dp[K%N-1];
    p(ans);
    return 0;
}