#include <fstream>

using namespace std;

int v[5000001], c[5000001];

int main()
{
    ifstream cin ("deque.in");
    ofstream cout ("deque.out");
    long long n, k, s, inc, sf;
    cin>>n>>k;
    inc=1;
    sf=0;
    s=0;
    for (int i=1; i<=n; i++)
    {
        cin>>v[i];
        if (i<k)
        {
            while (v[i]<v[c[sf]] && inc<=sf)
                --sf;
            c[++sf]=i;
        }
        else
        {
            if (c[inc]<i-k+1)
                inc++;
            while (v[i]<v[c[sf]] && inc<=sf)
                sf--;
            c[++sf]=i;
            s+=v[c[inc]];
        }
    }
    cout<<s;

    return 0;
}