#include <bits/stdc++.h>

using namespace std;

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

int main()
{
    long long n,k,s=0,a[5000001];
    deque<int> d;
    fin>>n>>k;
    for(int i=1;i<=n;i++){
        fin>>a[i];
        while(!d.empty() && a[d.back()]>a[i])
            d.pop_back();
        if(!d.empty() && d.front()==i-k)
            d.pop_front();
        d.push_back(i);
        if(i>=k)
            s+=a[d.front()];
    }
    fout<<s;
    return 0;
}