F - Dawid and Bags of Candies（枚举情况）

Dawid has four bags of candies. The i-th of them contains ai candies. Also, Dawid has two friends. He wants to give each bag to one of his two friends. Is it possible to distribute the bags in such a way that each friend receives the same amount of candies in total?
Note, that you can’t keep bags for yourself or throw them away, each bag should be given to one of the friends.
Input
The only line contains four integers a1, a2， a3and a4 (1≤ai≤100) — the numbers of candies in each bag.
Output
Output YES if it’s possible to give the bags to Dawid’s friends so that both friends receive the same amount of candies, or NO otherwise. Each character can be printed in any case (either uppercase or lowercase).
Examples
Input
1 7 11 5
Output
YES
Input
7 3 2 5
Output
NO
Note
In the first sample test, Dawid can give the first and the third bag to the first friend, and the second and the fourth bag to the second friend. This way, each friend will receive
12
12
candies.
In the second sample test, it’s impossible to distribute the bags.
四袋糖果，分给两个人，要求糖果数一样

#include
#include
#include
#include
#include
#include
using namespace std;
int a[5],ans=0;
int main()
{
    ios::sync_with_stdio(false);	
    for(int i=1;i<=4;i++)
    {
     cin>>a[i];	ans+=a[i];
	}
    if(ans%2) 
     cout<<"NO";
    else
    {
     ans/=2;
     for(int i=1;i<=4;i++)
      if(a[i]==ans)
      {
      	cout<<"YES";return 0;
	  }
     for(int i=1;i<=4;i++)
      for(int j=i+1;j<=4;j++)
	  if(a[i]+a[j]==ans)
	  {
	   cout<<"YES";return 0;	
	  } 
	  cout<<"NO";
	}
    return 0;
}