#include <fstream>
using namespace std;
const int NMAX=5000005;
int deq[NMAX], v[NMAX];
int main()
{
    ifstream in("deque.in");
    ofstream out("deque.out");
    int n, k, sum=0;
    in>>n>>k;
    for(int i=1; i<=n; i++)
        in>>v[i];
    int b=1, e=0;
    for(int i=1; i<=n; i++)
    {
        while(b<=e && v[i]<=v[deq[e]])
            e--;
        deq[++e]=i;
        if(i-k==deq[b])
            b++;
        if(i>=k)sum+=v[deq[b]];
    }
    out<<sum<<'\n';
    return 0;
}