#include <bits/stdc++.h>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");
int n, k, i, j, a;
long long s;
deque<pair<int,int>> v;

int main()
{
    f >> n >> k;
    for(i = 1; i <= n; i++)
    {
        f >> a;
        while(v.size() && v.back().first >= a) v.pop_back();
        while(v.size() && v.front().second == i - k) v.pop_front();
        v.emplace_back(a, i);
        if(i >= k)
            s += v.front().first;
    }
    g << s << "\n";
    return 0;
}