#include <bits/stdc++.h>

using namespace std;

ifstream fin  ("deque.in");
ofstream fout ("deque.out");

deque <int> q;
int n, k, v[5000005];
long long sol;

int main (){
    fin>>n>>k;
    for(int i=1; i<=n; i++){
        fin>>v[i];
        while(!q.empty() && v[i] <= v[q.back()])
            q.pop_back();
        q.push_back(i);

        if(i >= k){

            if(i - q.front() >= k)
                q.pop_front();

            sol += v[q.front()];
        }
    }
    fout<<sol;
    return 0;
}