#include <bits/stdc++.h>
#define ll long long
using namespace std;
deque <int> dq;
int v[5000005];
ifstream fin ("deque.in");
ofstream fout ("deque.out");
int main()
{
    ll sum=0;
    int n, k; fin>>n>>k;
    for (int i=1; i<=n; i++) fin>>v[i];
    for (int i=1; i<=n; i++) {
        while (!dq.empty()&&v[i]<=v[dq.back()])
            dq.pop_back();
        dq.push_back(i);
        if (dq.front()==i-k) dq.pop_front();
        if (i>=k) sum+=v[dq.front()];
    }
    fout<<sum;
    return 0;
}