#include <cstdio>
#include <deque>

using namespace std;

#define nr first
#define i second

deque < pair<int, int> > Q;
long N, K, x;
long long Rez;

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

    scanf("%ld %ld",&N, &K);
    for(int i = 1; i <= N; ++i)
    {
        scanf("%ld",&x);
        while(!Q.empty() && Q.back().nr > x) Q.pop_back();
        while(!Q.empty() && Q.front().i <= i - K) Q.pop_front();
        Q.push_back(make_pair(x, i));
        if(i >= K)
            Rez += Q.front().nr;
    }
    printf("%lld\n", Rez);
}