#include <iostream> using namespace std; int sum[100010],n,a[100010],k,ans; int main(){ cin>>n>>k; for(int i=1;i<=n;i++){ cin>>a[i]; sum[i]=sum[i-1]+a[i]; } for(int i=k;i<=n;i++) ans=max(ans,sum[i]-sum[i-k]); cout<<ans<<endl; return 0; }