Sereja and Bottles

Sereja and Bottles

Time Limit: 2000ms

Case Time Limit: 2000ms

Memory Limit: 262144KB

64-bit integer IO format: %I64d      Java class name: (Any)

Submit Status PID: 33596

Font Size:

Sereja and his friends went to a picnic. The guys had n soda bottles just for it. Sereja forgot the bottle opener as usual, so the guys had to come up with another way to open bottles.

Sereja knows that the i-th bottle is from brand a_i, besides, you can use it to open other bottles of brand b_i. You can use one bottle to open multiple other bottles. Sereja can open bottle with opened bottle or closed bottle.

Knowing this, Sereja wants to find out the number of bottles they've got that they won't be able to open in any way. Help him and find this number.

Input

The first line contains integer n (1 ≤ n ≤ 100) — the number of bottles. The next n lines contain the bottles' description. The i-th line contains two integers a_i, b_i (1 ≤ a_i, b_i ≤ 1000) — the description of the i-th bottle.

Output

In a single line print a single integer — the answer to the problem.

Sample Input

Input

4
1 1
2 2
3 3
4 4

Output

4

Input

4
1 2
2 3
3 4
4 1

Output

0

#include<iostream>
#include<cstdio>
#include<cstring>
using namespace std;
int a[1010],b[1010];
int mark[1010];
int main()
{
    int n,i,j,ans;
    while(cin>>n)
    {
        ans=0;
        memset(mark,0,sizeof(mark));
        for(i=0;i<n;i++)
        {
            cin>>a[i]>>b[i];
        }
        for(i=0;i<n;i++)
        {
            for(j=0;j<n;j++)
            {
                if(i!=j&&a[i]==b[j])
                {
                    mark[i]=1;
                }
            }
        }
        for(i=0;i<n;i++)
        {
            if(!mark[i])
            {
                ans++;
            }
        }
        cout<<ans<<endl;
    }
    return 0;
}