#include <fstream>
#include <deque>
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int i, j, n, m, k, v[5000002];
long long s;
deque<int> d;
int main() {
    cin>>n>>k;
    for(i=1;i<=n;i++){
        cin>>v[i];
    }
    d.push_back(1);
    for(i=2;i<k;i++){
         while(v[i]<v[d.back()]){
            d.pop_back();
        }
        d.push_back(i);
    }
    for(i=k;i<=n;i++){
        while(v[i]<v[d.back()]){
            d.pop_back();
        }
        d.push_back(i);
        if(i-d.front()+1==k+1)
            d.pop_front();
        s+=v[d.front()];
    }
    cout<<s;

}