#include <cstdio>
#include <deque>
using namespace std;

int n, k, a[5000005];
long long sum;
deque<int> d;

int main()
{

    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);

    scanf("%d%d", &n, &k);
    for(int i = 1; i <= n; ++i)
    {
        scanf("%d", &a[i]);

        while(!d.empty() && a[i] < d.back())
            d.pop_back();
        d.push_back(a[i]);

        if(i >= k && d.front() == a[i-k])
            d.pop_front();
        if(i >= k)
            sum += d.front();
    }

    printf("%lld", sum);

    return 0;
}