#include "bits/stdc++.h"
using namespace std;
     
#define DEBUG(x) cout<<#x<<": "<<x<<endl;
#define DEBUG_VEC(v) cout<<#v<<":";for(int i=0;i<v.size();i++) cout<<" "<<v[i]; cout<<endl
     
typedef long long ll;
#define vi vector<int>
#define vl vector<ll>
#define vii vector< vector<int> >
#define vll vector< vector<ll> >
#define vs vector<string>
#define pii pair<int,int>
#define pis pair<int,string>
#define psi pair<string,int>
#define pll pair<ll, ll>
const int inf = 1000000001;
const ll INF = 1e16;
#define MOD 1000000007
#define mod 1000000009
#define pi 3.14159265358979323846
#define Sp(p) cout<<setprecision(15)<<fixed<<p<<endl;
int dx[4] = { 1,0,-1,0 }, dy[4] = { 0,1,0,-1 };
int dx2[8] = { 1,1,0,-1,-1,-1,0,1 }, dy2[8] = { 0,1,1,1,0,-1,-1,-1 };


int main() {
  int n, k, i, j;
  cin >> n >> k;
  string s;
  cin >> s;
  string s2 = s + s;
  vector<pii> cnst(2 * n + 1);
  for (i = 0; i < 2 * n; i++) {
    cnst[i + 1] = cnst[i];
    if (cnst[i].second == 0) {
      cnst[i + 1].first++;
    }
    else {
      cnst[i + 1].second--;
    }
    cnst[i + 1].second += s2[i] - '0';
  }
  if (k <= 2 * n) {
    cout << cnst[k].first << endl;
    return 0;
  }

  int firstcnt = cnst[n].first;
  int firststock = cnst[n].second;
  int secondcnt = cnst[2 * n].first;
  int secondstock = cnst[2 * n].second;

  // DEBUG(firstcnt);
  // DEBUG(firststock);
  // DEBUG(secondcnt);
  // DEBUG(secondstock);

  
  if (firststock == secondstock) {
    int ans = firstcnt;
    int nokori = k - n;
    ans += nokori / n * (secondcnt - firstcnt);
    nokori %= n;
    ans += cnst[nokori].first;
    int stock = secondstock;
    if (stock > 0) {
      for (i = 0; i < nokori; i++) {
	if (cnst[i].second == 0) {
	  ans--;
	  stock--;
	  if (stock == 0) {
	    break;
	  }
	}
      }
    }
    cout << ans << endl;
    return 0;
    
  }
  else {
    string S;
    for (i = 0; i < 60; i++) {
      S += s;
    }
    int stock = 0, cnt = 0;
    i = 0;
    while (stock < 55 || i < k) {
      if (stock == 0) {
	cnt++;
      }
      else {
	stock--;
      }
      stock += S[i] - '0';
      i++;
    }
    cout << cnt << endl;
    return 0;
  }
  
  
}