#include<bits/stdc++.h>
using namespace std;

#define int long long

typedef long long ll;
typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
#define pb push_back
#define mp make_pair
#define fi first
#define se second
#define all(v) (v).begin(),(v).end()
#define rep(i,n) for(int i=0;i<(n);i++)
#define reps(i,f,n) for(int i=(f);i<(n);i++)
#define each(it,v) for(__typeof((v).begin()) it=(v).begin();it!=(v).end();it++)
template<class T,class U>void chmin(T &t,U f){if(t>f)t=f;}
template<class T,class U>void chmax(T &t,U f){if(t<f)t=f;}

int N,K;
string S;

int get(int k){
    int x=0,y=0;
    rep(i,k){
        if(x)x--;
        else y++;
        x+=S[i%N]-'0';
    }
    return y;
}

signed main(){
    cin>>N>>K>>S;

    if(K<10000){
        cout<<get(K)<<endl;
        return 0;
    }

    int x=0,y=0,yy=-114,yyy=-514;
    for(int i=0;true;i++){
        rep(j,N){
            if(x)x--;
            else y++;
            x+=S[j]-'0';
        }
        if(y-yy==yy-yyy){
            int tmp=K/N;
            int ans=y+(tmp-i-1)*(y-yy);
            tmp=K%N;
            rep(j,tmp){
                if(x)x--;
                else ans++;
                x+=S[j]-'0';
            }
            cout<<ans<<endl;
            return 0;
        }
        if(x>=N){
            cout<<y<<endl;
            return 0;
        }
    }
    return 0;
}