#include <fstream>

using namespace std;

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

int v[500000];
int dq[500000];
int n,k;

int main()
{
    cin>>n>>k;
    for(int i=0;i<n;i++){
        cin>>v[i];
    }
    int st = 0, dr = -1, s = 0;
    for(int i=0;i<n;i++){
        if(st<=dr && dq[st]==i-k){
            st++;
        }
        while(st<=dr && v[i]<=v[dq[dr]]){
            dr--;
        }
        dq[++dr]=i;
        if(i>=k-1){
            s+=v[dq[st]];
        }
    }
    cout<<s;
    return 0;
}