#pragma GCC optimize("unroll-loops,Ofast,O3")
#include <bits/stdc++.h>
#define pb push_back
#define mp make_pair
#define spc << " " <<
#define endl "\n"
#define all(x) x.begin(), x.end()
#define int long long
#define ii pair<int,int>
#define vi vector<int>
#define vii vector<ii>
#define st first
#define nd second
#define inf 1000000009
#define MOD 1000000007
#define lim 200005
using namespace std;
void solve(){
int n,d; cin >> n >> d;
int ans=0, cur=d+1;
for(int i=1; i<=n; i++){
int a; cin >> a;
if(a==1){
cur = i+d;
}
else if(i==cur){
ans++;
cur = i+d;
}
}
cout << ans << endl;
}
signed main(){
ios_base::sync_with_stdio(false);cin.tie(0);
#ifdef Local
freopen("in","r",stdin);
freopen("out","w",stdout);
#endif
int t=1;
//cin >> t;
while(t--) solve();
}
