#include <iostream>
#include <fstream>
using namespace std;
ifstream f("deque.in");
ofstream g("deque.out");

int n , m , a[600000] ;

int main()
{
   f >> n >> m ;
   for( int i = 1 ; i <= n ; i ++ )
    f >> a[i] ;
    int x = 99999999 ;
   for( int i = 1 ; i <= m ; i ++ )
     x = min(x , a[i]) ;
    int sum = x , cursor2 = m , cursor1 = 1 ;
   while( cursor2 < n )
       {
           if( a[cursor1] == x || x > a[cursor2 + 1] )
           {   x = 99999999 ;
               cursor1 ++ ;
               cursor2 ++ ;
               for( int i = cursor1 ; i <= cursor2 ; i ++ )
                x = min(x , a[i] ) ;
           }
           else {
            cursor1 ++ ;
           cursor2 ++ ;
           }
           sum += x ;
       }
       g << sum ;
}