#include <fstream>

using namespace std;
int n, i, u, p, v[5000003], d[5000003], k, s;
int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    fin>>n>>k;
    for(i=1;i<=n;i++)
        fin>>v[i];
    p=1;
    u=1;
    d[1]=1;
    for(i=2;i<=n;i++){
        while(v[i]<v[d[u]] && p<=u)
            u--;
        u++;
        d[u]=i;
        if(i-d[p]==k)
            p++;
        if(i>=k)
            s+=v[d[p]];
    }
    fout<<s;
    return 0;
}