/*
    https://infoarena.ro/problema/deque
*/

#include <bits/stdc++.h>

using namespace std;

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

int main(){
    int n, k, x;
    long long s = 0;

    f >> n >> k;
    int v[n], dq[n], st = 0, dr = -1;
    for(int i = 0; i < n; i++)
        f >> v[i];

    for(int i = 0; i < n; i++){
        if(st <= dr && dq[st] == i - k)
            st++;

        while(st <= dr && v[i] <= v[dq[dr]])
            dr--;

        dq[++dr] = i;
        if(i >= k - 1)
            s += v[dq[st]];
    }

    g << s;
}