#include<bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque<pair<int,int>>dequ;
int n,k;
int v[5000001];
long long s;
int main()
{
    f>>n>>k;
    for(int i=1;i<=n;i++)
        f>>v[i];
    dequ.push_back({ v[1],1} );
    for(int i=2;i<=k;i++)
    {
        while(!dequ.empty() && v[i]<=dequ.back().first)
            dequ.pop_back();
        dequ.push_back({v[i],i});
    }
    s=dequ.front().first;
    for(int i=k+1;i<= n;i++)
    {
        while(!dequ.empty() && v[i]<=dequ.back().first)
            dequ.pop_back();
        dequ.push_back({v[i],i});
        if(dequ.front().second==i-k)
            dequ.pop_front();
        s=s+dequ.front().first;
    }
    g<<s;
}