#include<bits/stdc++.h>

using namespace std;
using lint=long long;
#define rep(i,n) for(int i=0;i<int(n);++i)
int main(){
    int n,k;
    cin>>n>>k;
    vector<lint>a(n);
    rep(i,n)cin>>a[i];
    vector<lint>dp(n+1);
    vector<lint>b(n+1);
    rep(i,n)b[i+1]=b[i]+a[i];
    multiset<lint>s;
    s.emplace(0);
    for(int i=0;i<n;++i){
        dp[i+1]=max(dp[i],*s.rbegin()+b[i+1]);
        s.emplace(dp[i]-b[i+1]);
        if(i==k-2){
            s.erase(s.find(0));
        }if(i>=k-1){
            s.erase(s.find(dp[i-k+1]-b[i-k+2]));
        }
    }
    cout<<dp.back()<<endl;
}