#include <bits/stdc++.h>
using namespace std;
template<typename TH>
void _dbg(const char* sdbg, TH h) {
cerr << sdbg << " = " << h << "\n";
}
template<typename TH, typename... TA>
void _dbg(const char* sdbg, TH h, TA... t) {
while (*sdbg != ',') cerr << *sdbg++;
cerr << " = " << h << ",";
_dbg(sdbg + 1, t...);
}
#define db(...) _dbg(#__VA_ARGS__, __VA_ARGS__)
#define chkpt cerr << "------\n";
const int N=3e5+5;
int n,d,a[N];
int nxt[N];
int main() {
// freopen("COCI17_TELEFONI.INP","r",stdin);
ios_base::sync_with_stdio(0); cin.tie(0);
cin>>n>>d;
for(int i=1;i<=n;++i){
cin>>a[i];
}
nxt[n]=n+1;
for(int i=n-1;i>=1;--i){
nxt[i]=a[i+1]?(i+1):nxt[i+1];
}
int last=1;
while(last<=n){
if(nxt[last]-last>d){
break;
}
last=nxt[last];
}
int ans=0;
if(last!=n){
last+=d;
while(last!=n){
ans+=a[last]==0;
last+=d;
}
}
cout<<ans<<'\n';
return 0;
}
