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Write a program that reads the input and prints the answer. Run checks it against every test, including hidden ones.

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A building has n rooms numbered 0 to n-1. Some doors only open one way. A robot starts in room s. It can walk through any door in the direction the door opens.
How many rooms can the robot reach? Count room s itself.
Read the rooms and doors, then print that count.
Input. The first line holds n, m and s: the number of rooms (1 to 100000), the number of one-way doors (0 to 200000) and the start room. Each of the next m lines holds two integers a and b: a door from room a to room b.
Output. One integer: how many rooms the robot can reach from s, including s.
Example 1 input
```
5 4 0
0 1
1 2
3 4
2 0
```
Output
```
3
```
Example 2 input
```
4 0 2
```
Output
```
1
```
LanguageC++
#include <iostream> #include <vector> using namespace std; int main() { // Read the input from cin, work out the answer, and print it with cout. return 0; }