#include <iostream>
#include <deque>
#include <fstream>

#define NMAX 5000002

using namespace std;

int n,k,a[NMAX];
long long sol;

deque<int> d;

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

int main()
{
    f>>n>>k;
    d.push_back(1);
    for(int i=1;i<=n;i++){
        f>>a[i];
        while(!d.empty() && a[d.back()]>=a[i])
            d.pop_back();
        d.push_back(i);
        if(d.front()<=i-k)
            d.pop_front();
        if(i>=k)
            sol+=a[d.front()];
    }
    g<<sol;
    return 0;
}