#include <bits/extc++.h>
using namespace std;
using namespace __gnu_pbds;
#define ordered_set tree<int, null_type,less<int>, rb_tree_tag,tree_order_statistics_node_update>
void ALI_72(){
int n,d;
cin >> n >> d;
vector < int > v(n);
for(auto& i : v) cin >> i;
int ans = 0;
for(int i = 0;i < n;i+=d){
if(v[i] == 0){
ans++;
v[i] = 1;
}
}
if(v[n - 1] == 0) ans++;
cout << ans << '\n';
}
signed main()
{
ios_base :: sync_with_stdio(0);
cin.tie(0), cout.tie(0);
int t = 1;
//cin >> t;
while(t--){
ALI_72();
}
return 0;
}
