#include <fstream>
#include <iostream>

using namespace std;

ifstream fin ("deque.in");
ofstream fout ("deque.out");


int minime[5000000];
int N, K, v[5000000], s, f;
long long Sum;

int main()
{
    s = 1, f = 0;
    fin>>N>>K;
    for(int i  = 1; i <= N; i++)
    {
        fin>>v[i];
    }
    for(int i = 1; i<= N; i++)
    {
        while(s <= f && v[i] <= v[minime[f]])
        {
            f--;
        }
        minime[++f] = i;
        if(minime[s] == i-K)
        {
            s++;
        }
        if(i >= K)
        {
            Sum += v[minime[s]];
        }
    }
    fout<<Sum;

    return 0;
}