#include <bits/stdc++.h>
#define ll long long
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
deque <pair<ll,int>> coada;
int main()
{   int n,k;
    f>>n>>k;
    ll sum=0;
    for(int i=1; i<=n; i++)
    {   ll x;
        f>>x;
        bool ok=true;
        while(!coada.empty() && ok)
        {   ll ul=coada.back().first;
            ok=false;
            if(x<=ul)
            {   ok=true;
                coada.pop_back();
            }
        }
        coada.push_back({x,i});
        if(coada.front().second==i-k) coada.pop_front();
        if(i>=k) sum+=coada.front().first;
    }
    g<<sum;
    return 0;
}