#include <fstream>
#define ll long long
using namespace std;
ifstream cin ("deque.in");
ofstream cout ("deque.out");
int n;
int k;
int a[5000005];
int deq[5000005];
signed main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
    ll rasp = 0;
    int st = 1;
    int dr = 0;
    cin >> n >> k;
    for(int i=1;i<=n;i++)
        cin >> a[i];
    for(int i=1;i<=n;i++)
    {
        while(st<=dr && a[i]<=a[deq[dr]])
            dr--;
        deq[++dr] = i;
        if(deq[st] == i - k)
            st++;
        if(i>=k)
            rasp = rasp + (1LL*a[deq[st]]);
    }
    cout << rasp;
    return 0;
}