#include<bits/stdc++.h>
using namespace std;
#define rep(i,n) for(ll i=0;i<n;i++)
#define repl(i,l,r) for(ll i=(l);i<(r);i++)
#define per(i,n) for(ll i=(n)-1;i>=0;i--)
#define perl(i,r,l) for(ll i=(r)-1;i>=l;i--)
#define fi first
#define se second
#define pb push_back
#define ins insert
#define pqueue(x) priority_queue<x,vector<x>,greater<x>>
#define all(x) (x).begin(),(x).end()
#define CST(x) cout<<fixed<<setprecision(x)
#define rev(x) reverse(x);
using ll=long long;
using vl=vector<ll>;
using vvl=vector<vector<ll>>;
using pl=pair<ll,ll>;
using vpl=vector<pl>;
using vvpl=vector<vpl>;
const ll MOD=1000000007;
const ll MOD9=998244353;
const int inf=1e9+10;
const ll INF=4e18;
const ll dy[9]={1,0,-1,0,1,1,-1,-1,0};
const ll dx[9]={0,-1,0,1,1,-1,1,-1,0};
template<class T> inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return true;
    }
    return false;
}
template<class T> inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return true;
    }
    return false;
}
string s;
ll n;
ll solve(ll k,ll &now){
    ll ans=0;
    rep(i,k){
        if(now==0)ans++;
        else now--;
        now+=s[i%n]-'0';
    }
    return ans;
}
struct seen{
    ll pls,sum;
};
int main(){
    ll k;cin >> n >>k;
    string s;cin >> s;
    if(n<=10000000){
        ll hoge=0;
        cout << solve(k,hoge) <<endl;
        return 0;
    }
    vector<seen> v(n+1,{-1,-1});
    ll now=0,ans=0,repeat=0;
    v[0]={0,0};
    ll loopsum=-1;
    repl(t,1,10000){
        ans+=solve(n,now);
        if(v[now].pls!=-1){
            loopsum=ans-v[now].sum;
            ll rpt=k/n;
            rpt-=t;
            rpt/=t-v[now].pls;
            ans+=rpt*loopsum;
            repeat=t+rpt*(t-v[now].pls);
            repeat*=n;
            break;
        }
        v[now]={t,ans};
    }
    ans+=solve(k-repeat,now);
    cout << ans <<endl;
}