#include <string>
#include <vector>
#include <list>
#include <cmath>
#include <algorithm>
#include <deque>
#include <set>
#include <iostream>
#include <cstdio>
#include <cstdlib>
using namespace std;

class Graph {
  public:
    vector < vector <int> > Adj;
    vector <long long> Paths;
    vector <int> Incident;
    long long Num_Paths(int from, int to);
};

long long Graph::Num_Paths(int from, int to)
{
  long long rv;
  int i;

  if (from == to) return 1;
  
  rv = 0;
  for (i = 0; i < Adj[from].size(); i++) {
    rv += Num_Paths(Adj[from][i], to);
  }
  return rv;
}

int main()
{
  Graph G;
  int N;
  int from, to;
  int i;

  cin >> N;
  G.Adj.resize(N);
  G.Paths.resize(N);
  G.Incident.resize(N, 0);
  
  while (cin >> from >> to) {
    G.Adj[from].push_back(to);
    G.Incident[to]++;
  }
  cout << G.Num_Paths(0, N-1) << endl;
  exit(0);
  
}