#include <iostream>
#include <fstream>
using namespace std;
ifstream in ("deque.in");
ofstream out ("deque.out");
int N, K;
int A[5000002], Deque[5000002];
int Front, Back;
long long Sum;
 
int main()
{
    int i;
    in>>N>>K;
    for (i = 1; i <= N; i++) 
	{
		in>>A[i];
	}
    Front = 1; 
	Back = 0;
    for (i = 1; i <= N; i++)
    {
        while (Front <= Back && A[i] <= A[Deque[Back]]) 
		{
			Back--;
		}
        Deque[++Back] = i;
        if (Deque[Front] == i-K) Front++;
        if (i >= K) Sum += A[Deque[Front]];     
    }
	out<<Sum;
    return 0;
}