#include <fstream>

using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");

int v[5000001], coada[5000001];
int main()
{
    int i,n,k,inc,sf;
    long long s=0;
    cin>>n>>k;
    for(i=1;i<=n;i++)
        cin>>v[i];
    inc=1;
    sf=0;
    v[0]=-10000001;
    for(i=1;i<=k-1;i++)
    {
        while(v[i]<v[coada[sf]] && inc<=sf)
            sf--;
        sf++;
        coada[sf]=i;
    }
    for(i=k;i<=n;i++)
    {
        if(coada[inc]<i-k+1)
            inc++;
        while(v[i]<v[coada[sf]] && inc<=sf)
            sf--;
        sf++;
        coada[sf]=i;
        s=s+v[coada[inc]];
    }
    cout<<s;
    return 0;
}