#include <bits/stdc++.h>

#define maxn 5000010

using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

int n,k,v[maxn],maxime[maxn],st=1,dr;
long long int suma;

int main()
{
    f>>n>>k;
    for(int i=1; i<=n; i++)
        f>>v[i];
    int i=1;
    while(i<=n)
    {
        while(st<=dr && v[i]<v[maxime[dr]])
            dr--;
        maxime[++dr]=i;
        if(i-k== maxime[st])
            st++;
        if(i>=k)
            suma+=v[maxime[st]];
        i++;
    }
    g<<suma;
    return 0;
}