#include <stdio.h>
#include <stdlib.h>
long tab[5000001],a[5000001];
void quick_sort( int l , int r )
{
    int i , j;
    int x , aux;
    i = l;
    j = r;
    x = tab[ ( i + j ) / 2 ];
    do
    {
        while ( tab[ i ] < x )
            i++;
        while ( tab[ j ] > x )
            j--;
        if ( i <= j )
        {
            aux = tab[ i ];
            tab[ i ] = tab[ j ];
            tab[ j ] = aux;
            i++;
            j--;
        }
    } while ( i <= j );
    if ( l < j )
        quick_sort( l , j );
    if ( r > i )
        quick_sort( i , r );
}




int main()
{
    int i,n,k,j,ll;

    long long s=0;
   freopen("deque.in","r",stdin);
   freopen("deque.out","w",stdout);
   scanf("%i %i",&n,&k);
    for(i=0;i<n;i++)
    scanf("%li",&a[i]);
ll=0;
while(ll+k<=n){
    for(i=ll,j=0;i<ll+k;i++,j++)
        tab[j]=a[i];
    quick_sort(0,k-1);
    s+=tab[0];
   // printf(".");
    ll++;
}
printf("%lli",s);

    return 0;
}