#include <fstream>
using namespace std;

ifstream f("deque.in");
ofstream g("deque.out");

const int NMAX=5000001;

int N,K,x;
long long S;

int v[NMAX],DQ[NMAX];

long long solve()
{
    f>>N>>K;
    for(int i=1;i<=N;i++)
        f>>v[i];
    int f=1,b=0;
    for(int i=1;i<=N;i++)
    {
        //
        while(f<=b&&v[i]<=v[DQ[b]])
            b--;
        //
        DQ[++b]=i;
        if(DQ[f]==i-K)
            f++;
        if(i>=K)
            S+=v[DQ[f]];
    }
    return S;
}

int main()
{
    g<<solve();
    return 0;
}