#include <iostream>

using namespace std;

const int N = 5000000;

int v[N], d[N];

int main()
{
    int n, k, st = 0, sum = 0, dr = -1;
    cin >> n >> k;
    for (int i = 0; i < n; ++i) {
        cin >> v[i];
        while(st <= dr && d[st] == i - k) {
            ++st;
        }
        while(st <= dr && v[i] <= v[d[dr]]) {
            --dr;
        }
        d[++dr] = i;
        if( i >= k - 1) {
            sum += v[d[st]];
        }
    }
    cout << sum;
    return 0;
}