#include<fstream>
#include<limits.h>
#define maxn 5000000
using namespace std;
ifstream cin("deque.in");
ofstream cout("deque.out");
int a[maxn];
int  n, k, i, s=0, j;
int man;
int main()
{

    cin>>n>>k;
    for(i=1; i<=n; i++)
    {
        cin>>a[i];
    }
for(i=1; i<=n-k+1; i++)
{
man=INT_MAX;
     for(j=0; j<k; j++)
     if(a[i+j]<man)
     man=a[i+j];
     s=s+man;
}
cout<<s;
    cin.close();
    cout.close();
    return 0;
}