ctf_a_f.py

#! /usr/bin/env python
# -*- coding: utf-8 -*-
 
import os
import sys
 
class Hoge(object):
    
    def __init__(self):
        pass
 
    def func(self):
        '''
        insert your code
        '''
        n, m = map(int, raw_input().split())
        info = []
        high = []
        for i in range(m):
            a, b = map(int, raw_input().split())
            info.append((a, b))
            if b == 1:
                high.append(a)
 
 
        while True:
            flg = False
            for a, b in info:
                # print a, b
                # print high
                if b in high and not a in high:
                    high.append(a)
                    # print a
                    flg = True
            if flg == True:
                continue
            else:
                break
 
        # print high
        print len(high) + 1
        return None
 
if __name__ == '__main__':
    h = Hoge()
    h.func()