#include <bits/stdc++.h>
#define FOR(i,a,b) for (int i=(a);i<(b);i++)
#define FORR(i,a,b) for (int i=(a);i>=(b);i--)
#define pb push_back
#define pcnt __builtin_popcount
#define show(x) cout<<#x<<" = "<<x<<endl;
#define maxs(x,y) x = max(x,y)
#define mins(x,y) x = min(x,y)
#define fi first
#define se second
#define rng(a) a.begin(),a.end()
#define each(it,c) for(__typeof((c).begin()) it=(c).begin();it!=(c).end();it++)
#define sz(x) (int)(x).size()
#define mp make_pair

using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<pii> vpii;
typedef set<int> si;
typedef pair<ll,ll> pll;
typedef vector<ll> vl;
typedef vector<vl> vvl;
typedef vector<pll> vpll;
typedef set<ll> sl;
template<typename T>string join(vector<T>&v)
{stringstream s;FOR(i,0,sz(v))s<<' '<<v[i];return s.str().substr(1);}
ll gcd(ll a,ll b){if(a>b)swap(a,b);for(;a>0;b%=a,swap(a,b));return b;}
int modpow(ll a,ll n,int m){if(a==0)return a;ll p=1;for(;n>0;n/=2,a=a*a%m)if(n&1)p=p*a%m;return(int)p;}
void dout(double d){printf("%.12f\n",d);}

const int iinf = 1e9;
const ll linf = 1e18;
const int mod = 1e9+7;
const double pi = acos(-1);
const double eps = 1e-10;
ll n, k;
string s;
pll cyc(ll a, ll r){
  ll b = 0;
  FOR(i, 0, a){
    if(r < 1){
      b++;
      r++;
    }
    r--;
    r += s[i] - '0';
  }
  return mp(b, r);
}
main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> k >> s;
  pll t, t2;
  if(k <= n){
    cout << cyc(k, 0).fi;
  }else if(k <= n * 2){
    t = cyc(n, 0);
    cout << t.fi + cyc(k-n, t.se).fi;
  }else{
    t = cyc(n, 0);
    t2 = cyc(n, t.se);
    ll ans = t.fi + t2.fi * (k / n - 1) + cyc(k%n, t2.se).fi;
    cout << ans;
  }
  cout << endl;
  return 0;
}