#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ld = long double;
using ull = unsigned long long;

#define rep(i,n) for(ll i=0;i<n;++i)
#define all(a) (a).begin(),(a).end()
ll intpow(ll a, ll b){ ll ans = 1; while(b){ if(b & 1) ans *= a; a *= a; b /= 2; } return ans; }
ll modpow(ll a, ll b, ll p){ ll ans = 1; while(b){ if(b & 1) (ans *= a) %= p; (a *= a) %= p; b /= 2; } return ans; }
template<class T> T div_floor(T a, T b) { return a / b - ((a ^ b) < 0 && a % b); }
template<class T> T div_ceil(T a, T b) { return a / b + ((a ^ b) > 0 && a % b); }
template <typename T, typename U> inline bool chmin(T &x, U y) { return (y < x) ? (x = y, true) : false; }
template <typename T, typename U> inline bool chmax(T &x, U y) { return (x < y) ? (x = y, true) : false; }


void solve() {
    ll N,A;
    cin>>N>>A;
    string S;
    cin>>S;
    ll rank=0;
    ll event=0;
    ll ac=0;
    rep(_,N){
        if (S[event%N]=='0'){
            rank++;
        }
        else{
            if (rank!=0){
                rank--;
                ac++;
                if (ac==A){
                    cout<<event+1<<endl;
                    return;
                }
            }
        }
        event++;
    }
    ll cnt0=count(all(S),'0');
    ll cnt1=count(all(S),'1');
    ll loop=(A-1-ac)/min(cnt0,cnt1);
    ac+=loop*min(cnt0,cnt1);
    event+=loop*N;
    if (cnt0>cnt1){
        rank=1e9;
    }
    rep(_,N){
        if (S[event%N]=='0'){
            rank++;
        }
        else{
            if (rank!=0){
                rank--;
                ac++;
                if (ac==A){
                    cout<<event+1<<endl;
                    return;
                }
            }
        }
        event++;
    }
    assert (false);
    return;
}


int main() {
    ll T=1;
    while (T--){
        solve();
    }
    return 0;
}