it is not easy

#include <bits/stdc++.h>
using namespace std ; 

int v , n , w[20005] , f[100005]  ;

int main()
{
	cin >> v >> n ;
	for( int i = 1 ; i <= n ; i ++ )
	{
		cin >> w[i] ;
	}
	for(int i = 1 ; i <= n ; i ++ )
	{
        for( int j = v ; j >= w[i] ; j -- )
		{                           
            if( f[j] < f[j - w[i]] + w[i] )
			{
                f[j] = f[j - w[i]] + w[i] ;
            }
        }
    }
	cout << v - f[n] ;
	return 0 ;
}