#include <cstdio>

using namespace std;
int d[5000005],v[5000005];
int main()
{
    FILE *fin=fopen ("deque.in","r");
    FILE *fout=fopen ("deque.out","w");
    int n,k,i,p,u;
    long long s=0;
    fscanf (fin,"%d%d",&n,&k);
    for (i=1;i<=n;i++)
        fscanf (fin,"%d",&v[i]);
    d[1]=1;
    p=1;
    u=1;
    for (i=2;i<=n;i++){
        while (p<=u && v[i]<=v[d[u]])
            u--;
        u++;
        d[u]=i;
        if (i-d[p]==k)
            p++;
        if (i>=k){
            s+=v[d[p]];
            //printf ("%d ",v[d[p]]);
        }
    }
    fprintf (fout,"%lld",s);
    return 0;
}