#include <bits/stdc++.h>
#define GLHF ios_base::sync_with_stdio(0); cin.tie(), cout.tie();
#define GGWP return 0;
#define ALTF4 exit(0)
#define GCWS/*Good Contest, Well Solved*/ ALTF4
#define ull unsigned long long
#define ll long long
#define ld long double
#define fxr1(x) for(int I = 0; I < x; ++I)
#define fxr(x) for(int I = 0; I <= x; ++I)
using namespace std;
int n, d, ans, cnt;
bool a[300001];
int main()
{
GLHF
cin >> n >> d;
for ( int I = 0; I < n; ++I )
{
cin >> a[I];
if ( a[I] == 0 )
++cnt;
else
cnt = 0;
if ( cnt == d )
{
++ans;
a[I] = 1;
cnt -= d;
}
}
cnt = 1;
for ( int I = 0; I < n - 2; ++I )
{
if ( a[I] == 0 )
{
++cnt;
}
}
cout << ans << endl;
GGWP
}
//clang++ -v -std=c++11 finish fishing the fish.people
