#include <bits/stdc++.h>

using namespace std;

deque <int> d;
int n, x, k, nr, h, a[5000005];
long long s;

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

int main()
{
    f >> n >> k;
    for(int i=1; i<=n; i++)
    {
        f >> a[i];
        while(!d.empty() && d.back()<=i-k) d.pop_back();
        while(!d.empty() && a[d.front()]>a[i]) d.pop_front();
        d.push_front(i);
        if(i>=k) s+=a[d.back()];
    }
    g << s;
}