#include <iostream>

using namespace std;

int main()
{
    int sum = 0;
    int num;
    int x[999];
    int y[999];
    bool check = true;
    int r = 0;

    cin >> num;

    for(int i = 0; i < num; ++i)
    {
        r = scanf("%d %d", &x[i], &y[i]);
    }

    r = r + r;

    for(int i = 0; i < num; ++i)
    {
        check = true;

        if(x[i] != y[i])
        {
            for(int j = 0; j < num; ++j)
            {
                if(j != i)
                {
                    if(x[i] == x[j] && y[i] == y[j])
                    {
                        check = false;
                    }

                    if(x[i] == y[j] && y[i] == x[j])
                    {
                        check = false;
                    }
                }
            }

            if(check)
            {
                ++sum;
            }
        }
    }

    cout << sum << char(10);
}