#include <fstream>
#include <deque>
using namespace std;

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

deque<int> q;
int v[5000005];

int main(){
    int n,k,sum=0;
    cin>>n>>k;
    for (int i=1; i<=n; i++) {
        cin>>v[i];
        while (!q.empty() && v[i]<v[q.back()]) {
            q.pop_back();
        }
        q.push_back(i);
        if (i>=k) {
            while (q.front()<i-k+1){
                q.pop_front();
            }
            sum+=v[q.front()];
        }
    }
    cout<<sum;
}