#include <bits/stdc++.h>
using namespace std;
ifstream fin("deque.in");
ofstream fout("deque.out");
int n, k, v[5000001];
long long sum;
deque<int> q;
int main(){
    fin>>n>>k;
    for(int i=1; i<=n; i++)
        fin>>v[i];
    for(int i=1; i<=n; i++){
        while(!q.empty() && v[i] <= v[q.back()]) q.pop_back();
        q.push_back(i);
        if(q.front() == i-k) q.pop_front();
        if(i >= k) sum += v[q.front()];
    }
    fout<<sum<<"\n";
}