#include <cstdio>
#include <algorithm>
#include <cstring>
using namespace std;
int v[5000005],dq[5000005],n,k;
long long sum;
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    scanf("%d %d",&n,&k);
    int B=0,F=1;
    for (int i=1;i<=n;i++)
    {
        scanf("%d",&v[i]);
        while (v[i]<=v[dq[B]] && B>=F) --B;
        dq[++B]=i;
        if (dq[F]==i-k) ++F;
        if (i>=k) sum+=v[dq[F]];
    }
    printf("%lld",sum);
    return 0;
}