#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

 int n, k, a[5000001], b[5000001], x, mini, nr=0, fr=1, bk=0;
long long suma;
int main()
{  f>>n>>k;
    for(int i=1; i<=n; i++)
        f>>a[i];
    for(int i=1; i<=n; i++)
    {
        while(fr<=bk && a[i]<=a[b[bk]])
            bk--;
        bk++;
        b[bk]=i;
        if(b[fr]==i-k)
            fr++;
        if(i>=k)
            suma=suma+a[b[fr]];
    }
    g<<suma;
    return 0;
}