#include <cstdio>
#include <cstdlib>
#define N 5000000

using namespace std;
int v[N], d[N];

int main()
{
    int st, dr, n, k, i;
    long long s;
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    scanf("%d%d", &n, &k);
    s = 0;
    st = 0;
    dr = -1;
    for(i = 0; i < n; i++) {
        scanf("%d", &v[i]);
        if(st <= dr && d[st] == i - k) {
            st++;
        }
        while(st <= dr && v[i] <= v[d[dr]]) {
            dr--;
        }
        d[++dr] = i;
        if(i >= k - 1) {
            s += v[d[st]];
        }
    }
    printf("%lld", s);
    return 0;
}