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voyage2 Batch , stdin/stdout

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voyage2.html

voyage2

Problem Statement

In Takahashi Kingdom, there is an archipelago of N islands, called Takahashi Islands. For convenience, we will call them Island 1, Island 2, ..., Island N.

There are M kinds of regular boat services between these islands. Each service connects two islands. The i-th service connects Island ai and Island bi.

Cat Snuke is on Island 1 now, and wants to go to Island N. However, it turned out that there is no boat service from Island 1 to Island N, so he wants to know whether it is possible to go to Island N by using two boat services.

Help him.

Constraints

  • 3 ≤ N ≤ 200 000
  • 1 ≤ M ≤ 200 000
  • 1 ≤ ai < bi ≤ N
  • (ai, bi) ≠ (1, N)
  • If i ≠ j, (ai, bi) ≠ (aj, bj).

Input

Input is given from Standard Input in the following format:

N M
a1 b1
a2 b2
:
aM bM

Output

If it is possible to go to Island N by using two boat services, print POSSIBLE; otherwise, print IMPOSSIBLE.

Sample Input 1

3 2
1 2
2 3

Sample Output 1

POSSIBLE

Sample Input 2

4 3
1 2
2 3
3 4

Sample Output 2

IMPOSSIBLE

You have to use three boat services to get to Island 4.

Sample Input 3

100000 1
1 99999

Sample Output 3

IMPOSSIBLE

Sample Input 4

5 5
1 3
4 5
2 3
2 4
1 4

Sample Output 4

POSSIBLE

You can get to Island 5 by using two boat services: Island 1 -> Island 4 -> Island 5.

Tags

Graph Theory

Subtasks and Limits

Subtask Score #TC Time Memory Scoring
1100111s256MBMinimum
2041s256MBMinimum

Judge Compile Command

g++-8 ans.cpp -o voyage2 -Wall -Wshadow -static -O2 -lm -m64 -s -w -std=gnu++17 -fmax-errors=512

Accepted Submissions

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Past Submissions

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mrJudge 09.05.20
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