#include <fstream>

using namespace std;

int n,i,k,v[5000001],p,u,d[5000001];

long long s;

ifstream fin ("deque.in");

ofstream fout ("deque.out");

int main (){

    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 (p<=u && v[i] <= v[d[u]]){
            u--;
        }
        d[++u] = i;
        if (i- d[p] == k)
            p++;

        if (i >= k)
            s+=v[d[p]];
    }
    fout<<s;

    return 0;
}