#include<iostream>
#include<fstream>
 using namespace std;
#define m 5000010
#define m1 1000000000
  
int n, k;
int a[m];
long long s;
  
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 = m1;
        for (j = 0; j < k; j++)
            if (a[i+j] < b) 
		b = a[i+j];
  
        s+= b;
    }
  
    g<<s;
     f.close();
     g.close();
    return 0;
}