#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
#define ll long long
const long long mod=998244353;
const long long hmod=46216567629137;
int main(){
    cin.tie(0)->sync_with_stdio(0);
    cout.tie(0);
    ll N,A;
    string S;
    cin>>N>>A>>S;
    int zero=0,one=0;
    rep(i,N){
        if(S[i]=='0') zero++;
        else one++;
    }
    int maximum=0;
    int now=0;
    rep(i,N){
        if(S[i]=='0') now--;
        else now++;
        maximum=max(maximum,now);
    }
    ll ans=0;
    if(one-maximum-zero>=0){
        ll cnt=(A-1)/(one-maximum);
        ans+=N*cnt;
        cnt*=(one-maximum);
        int now=1200;
        rep(i,N){
            if(cnt==A) break;
            if(S[i]=='1'){
                if(now!=1200){
                    now++;
                    cnt++;
                }
            }
            else now--;
            ans++;
        }
        cout<<ans<<endl;
        return 0;
    }
    else{
        ll now_rate=1200;
        ll ans=0;
        ll cnt=0;
        while(now_rate>=1200-maximum){
            ans+=N;
            cnt+=one-(maximum-1200+now_rate);
            if(cnt>A){
                cnt-=one-0LL,(maximum-1200+now_rate);
                ans-=N;
                break;
            }
            now_rate+=one-(maximum-1200+now_rate)-zero;
        }
        ll loop=(A-cnt-1)/one;
        ans+=N*loop;
        cnt+=loop*one;
        rep(i,N){
            if(cnt==A) break;
            if(S[i]=='1'){
                cnt++;
            }
            ans++;
        }
        cout<<ans<<endl;
    }
}