#include<iostream>
#include<fstream>
 using namespace std;
#define m 5000010
#define maz 1000000000
 
int N, K;
int A[m];
long long Sum;
 
int main()
{
    ifstream f("deque.in");
	ofstream g("deque.out");
 
    int i, j, b;
 
    f>>N>>K;
 
    for (i = 1; i <= N; i++) f>>A[i];
 
    for (i = 1; i <= N-K+1; i++)
    {
        b = maz;
        for (j = 0; j < K; j++)
            if (A[i+j] < b) b = A[i+j];
 
        Sum += b;
    }
 
    g<<Sum;
	 f.close();
	 g.close();
    return 0;
}