#include <cstdio>
using namespace std;
int v[5000001],c[5000001];
int main()
{
    freopen("deque.in","r",stdin);
    freopen("deque.out","w",stdout);
    int n,k,i,p,u;
    long long s=0;
    scanf("%d%d",&n,&k);
    for(i=1;i<=n;i++)
        scanf("%d",&v[i]);
    p=1;u=1;c[1]=1;
    for(i=2;i<=n;i++)
    {
        while(v[i]<=v[c[u]]&&u>=p)
            u--;
        u++,c[u]=i;
        if(c[p]==i-k)
            p++;
        if(i>=k)
            s+=v[c[p]];
    }
    printf("%lld",s);
    return 0;
}