#include <iostream>
#include <fstream>
#include <deque>
using namespace std;
ifstream f ("deque.in");
ofstream g ("deque.out");
deque<long long> dq;
long long v[5000001];
long long n,k,suma;
int main()
{
    f >> n >> k;
    for(int i = 1; i<=n; i++)
    {
        f >> v[i];
        while(!dq.empty() && v[dq.back()]>v[i])
        {
            dq.pop_back();
        }
        if(!dq.empty() && dq.front() == i - k)
        {
            dq.pop_front();
        }
        dq.push_back(i);
        if(i>=k)
            suma+=v[dq.front()];
    }
    g << suma;

}