#include <bits/stdc++.h>

using namespace std;

const int MAXN = 5000005;

int v[MAXN];
deque<int> d;

int main()
{
    ifstream fin("deque.in");
    ofstream fout("deque.out");
    int n, k;
    fin >> n >> k;
    for(int i = 1; i <= n; ++i)
        fin >> v[i];
    long long sum = 0;
    for(int i = 1; i <= n; ++i){
        while(!d.empty() && v[i] < v[d.back()])
            d.pop_back();
        if(!d.empty() && i - d.front() + 1 > k)
            d.pop_front();
        d.push_back(i);
        if(i >= k)
            sum += 1LL * v[d.front()];
    }
    fout << sum;
    return 0;
}