#include <bits/stdc++.h>

using namespace std;

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

const int DIM = 5e6 + 5;
int n, k, v[DIM];
long long suma;

deque <int> q;

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){
            suma += v[q.front()];
            if(i >= k && q.front() == i-k+1)
                q.pop_front();
        }
    }

    fout<<suma;
    return 0;
}