#include <bits/stdc++.h>

using namespace std;

long long int n , i , k , x , a[5000005] , p , u , s;
deque <long long int> q;

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

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