#include <bits/stdc++.h>
#define MAX 5000002
using namespace std;
int n,v[MAX],k;
long long ans;
deque<int> dq;

ifstream fin("deque.in");
ofstream fout("deque.out");

int main()
{
    fin >> n >> k;
    for(int i = 1; i <= n; i++){
        fin >> v[i];
        while(!dq.empty() && v[dq.back()] >= v[i]){
            dq.pop_back();
        }
        dq.push_back(i);
        if(dq.front() <= i-k){
            dq.pop_front();
        }
        if(i >= k){
            ans += v[dq.front()];
        }
    }
    fout << ans;
    return 0;
}