C++ :

#include<bits/stdc++.h>
using namespace std;
int n,k,a[1000001],b[1000001],c[1000001],sum0,sum1,ans;
int main()
{
//	freopen("8.in","r",stdin);
	cin>>n>>k;
	for(int i=1;i<=n;i++)
		cin>>a[i];
	for(int i=1;i<=n;i++){
		if(a[i]==0) sum0++;
		b[i]=sum0;
	}	
	for(int i=1;i<=n;i++){
		if(a[i]==1) sum1++;
		c[i]=sum1;
	}
	for(int i=1;i<=n-k+1;i++){
		if((c[i+k-1]-c[i-1])<(b[i+k-1]-b[i-1])) ans++;
	}
	cout<<ans;
	return 0;
}