#include <cstdio>
#include <deque>

using namespace std;

int N, K;
deque<pair<int, int> > v;

int main()
{
    freopen("deque.in", "rt", stdin);
    freopen("deque.out", "wt", stdout);

    scanf("%d %d", &N, &K);
    long long sum = 0;
    for (int i = 0; i < N; i++)
    {
        int val;
        scanf("%d", &val);

        for (; !v.empty() && v.back().first > val; )
            v.pop_back();
        v.push_back(make_pair(val, i));
        if (i - v.front().second + 1 > K)
            v.pop_front();

        if (i >= K - 1)
            sum += v.front().first;
    }
    printf("%lld\n", sum);

    return 0;
}