#include<bits/stdc++.h>
#define ll long long
#define nxm 5000005
using namespace std;

int n, m, a[nxm], deq[nxm];

int main(){
    cin.tie(0);
    ios::sync_with_stdio(0);
	int n, m;
	cin >> n >> m;
	for (int i = 1; i <= n; ++i) {
		cin >> a[i];
	}
	int front = 1, back = 0;
	ll sum = 0;
	for (int i = 1; i <= n; ++i) {
		while(front <= back && a[i] <= a[deq[back]]) {
			back--;
		}
		back++;
		deq[back] = i;
		if (deq[front] == i - m) {
			front++;
		}
		if (i >= m) {
			sum += a[deq[front]];
		}
	}
	cout << sum;
    return 0;
}