#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n;
  ll a;
  cin >> n >> a;
  string s;
  cin >> s;
  int imx = 0, mx = 0, acc = 0;
  rep(i, n) {
    if (s[i] == '0') acc--;
    else {
      acc++;
      if (chmax(mx, acc)) imx = i + 1;
    }
  }
  ll ans = 0;
  ll now = 1200;
  for (int i = 0; i < imx && a;) {
    if (s[i] == '0') now--;
    else if (now < 1200) now++, a--;
    ans++, i++;
  }
  rotate(s.begin(), s.begin() + imx, s.end());
  int diff = n - 2 * count(all(s), '0');
  int minus = max(0, diff);
  int gain = count(all(s), '1') - minus;
  assert(gain > 0);
  ll q = a / gain;
  a %= gain;
  ans += n * q;
  now += min(0, diff) * q;
  for (int i = 0; a;) {
    if (s[i] == '0') now--;
    else if (now < 1200) now++, a--;
    ans++, i++;
  }
  cout << ans << '\n';
}