#include <cstdio>
#include <cstring>
#include <algorithm>
#define maxN 5000002
using namespace std;
int n, i, j, k, st, dr;
long long sum, v[maxN];
int d[maxN];
void left(int i)
{
    if (i - d[st] == k)
        ++ st;
}
void right(int i)
{
    while (st <= dr && v[i] <= v[d[dr]])
        -- dr;
    d[++ dr] = i;
}
void write()
{
    freopen("deque.out", "w", stdout);
    printf("%lld", sum);
}
void read()
{
    freopen("deque.in", "r", stdin);
    scanf("%d %d", &n, &k);
    st = 1;
    for (i = 1; i <= n; ++ i)
    {
        scanf("%lld", &v[i]);
        left(i);
        right(i);
        if (i >= k)
           sum += v[d[st]];
    }
}
int main()
{
    read();
    write();
    return 0;
}