#include <iostream>
#include <fstream>
#define Maxx 5000005
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int p,u,D[Maxx],A[Maxx],i,n,k;
long long ans;
int main()
{
    fin>>n>>k;
    for (i=1;i<=n;i++)
        fin>>A[i];
    p=1;
    u=0;
    for (i=1;i<=n;i++)
    {
        while (p<=u && A[i]<=A[D[u]])
            u--;
        D[++u]=i;
        if (D[p]==i-k)
            p++;
        if (i>=k)
            ans+=A[D[p]];
    }
    fout<<ans;
    return 0;
}