#include <iostream>
#include <bits/stdc++.h>

using namespace std;
ifstream r("deque.in");
ofstream w("deque.out");
deque<int>d;
int v[5000002];
int main()
{
    int n, k;
    long long sum=0;
    r>>n>>k;
    for(int i=0;i<k;i++){
        r>>v[i];
        while(d.size()!=0 && v[i]<d.back()){
            d.pop_back();
        }
        d.push_back(v[i]);
    }
    sum+=d.front();
    for(int i=k;i<n;i++){
        r>>v[i];
        if(v[i-k]==d.front()){
            d.pop_front();
        }
        while(d.size()!=0 && v[i]<d.back()){
            d.pop_back();
        }
        d.push_back(v[i]);
        sum+=d.front();
    }
    w<<sum;
    return 0;
}