#include <cstdio>
#include <deque>
using namespace std;
deque<int> V;
long long sum;
int n, A[5000010], k;
void citire()
{
    int i;
    scanf("%d%d", &n, &k);
    for(i=1;i<=n;++i)
        scanf("%d", &A[i]);
}
void rezolva_problema()
{
    int i;
    citire();
    for(i=1;i<=n;++i)
    {
        while(!V.empty()&&A[V.back()]>=A[i])
            V.pop_back();
        V.push_back(i);
        if(V.front()==i-k) V.pop_front();
        if(i>=k) sum=sum+A[V.front()];
    }
    printf("%lld\n", sum);
}
int main()
{
    freopen("deque.in", "r", stdin);
    freopen("deque.out", "w", stdout);
    rezolva_problema();
    return 0;
}