#include <stdio.h>

int d[5000000];
int v[5000000];

int main()
{
    FILE *fin, *fout;
    int n, k;
    int i, st, dr;
    long long sum;

    fin = fopen("deque.in", "r");
    fscanf(fin, "%d%d", &n, &k);
    for (i = 0; i < n; i++) {
        fscanf(fin, "%d", &v[i]);
    }
    fclose(fin);

    st = 0;
    dr = -1;
    sum = 0LL;
    for (i = 0; i < n; 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)
            sum += v[d[st]];
    }

    fout = fopen("deque.out", "w");
    fprintf(fout, "%lld", sum);
    fclose(fout);
    return 0;
}