#include <bits/stdc++.h>
#include <cstdio>
#include <deque>
using namespace std;

int n,i,k,a[5000005];
long long s;
deque<int>d;
int main()
{
    ifstream f("deque.in");
    ofstream g("deque.out");
    f>>n>>k;
    for(i=1; i<=n; i++)
    {
        f>>a[i];
        while(!d.empty()&&a[d.back()]>=a[i])
            d.pop_back();
        d.push_back(i);
        if(i-d.front()==k) d.pop_front();
        if(i>=k)s=s+a[d.front()];
    }
    g<<s;
    return 0;
}