#include <stdio.h>
#include <stdlib.h>
#define N 5000000

int v[N], d[N];

int main()
{
    int st, dr, n, k, i;
    long long s;
    FILE *in, *out;
    in = fopen("deque.in", "r");
    out = fopen("deque.out", "w");
    fscanf(in, "%d%d", &n, &k);
    s = 0;
    st = 0;
    dr = -1;
    for (i = 0; i < n; i++)
    {
        fscanf(in, "%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]];
        }
    }
    fclose(in);
    fprintf(out, "%lld", s);
    fclose(out);
    return 0;
}