#include <bits/stdc++.h>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
int main()
{
    int n,i,k;
    long long s = 0;
    deque <int> dq;
    in >> n >> k;
    vector <int> v(n);
    for(i = 0;i < n;i++){
        in >> v[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 - 1)
            s += v[dq.front()];
    }
    out << s;
    return 0;
}