#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream in("deque.in");
ofstream out("deque.out");
const int maxn = 5000005;
deque <int> dq;
int v[maxn];

int main()
{
    int n, k;
    in >> n >> k;
    for(int i = 1; i <= n; i++)
        in >> v[i];
    for(int i = 1; i < k; i++)
    {
        while(!dq.empty() && v[dq.back()] >= v[i])
            dq.pop_back();
        dq.push_back(i);
    }
    long long sum = 0;
    for(int i = k; i <= n; i++)
    {
        while(i - dq.front() + 1 > k)
            dq.pop_front();
        while(!dq.empty() && v[dq.back()] >= v[i])
            dq.pop_back();
        dq.push_back(i);
        sum = sum + v[dq.front()];
    }
    out << sum << "\n";
    return 0;
}