A9399. Guess a number!
编程题
普及/提高-
知识点
题目描述
A TV show called "Guess a number!" is gathering popularity. The whole Berland, the old and the young, are watching the show.
The rules are simple. The host thinks of an integer $y$ and the participants guess it by asking questions to the host. There are four types of acceptable questions:
- Is it true that $y$ is strictly larger than number $x$ ?
- Is it true that $y$ is strictly smaller than number $x$ ?
- Is it true that $y$ is larger than or equal to number $x$ ?
- Is it true that $y$ is smaller than or equal to number $x$ ?
On each question the host answers truthfully, "yes" or "no".
Given the sequence of questions and answers, find any integer value of $y$ that meets the criteria of all answers. If there isn't such value, print "Impossible".
The rules are simple. The host thinks of an integer $y$ and the participants guess it by asking questions to the host. There are four types of acceptable questions:
- Is it true that $y$ is strictly larger than number $x$ ?
- Is it true that $y$ is strictly smaller than number $x$ ?
- Is it true that $y$ is larger than or equal to number $x$ ?
- Is it true that $y$ is smaller than or equal to number $x$ ?
On each question the host answers truthfully, "yes" or "no".
Given the sequence of questions and answers, find any integer value of $y$ that meets the criteria of all answers. If there isn't such value, print "Impossible".
输入格式
The first line of the input contains a single integer $n$ ( $1<=n<=10000$ ) — the number of questions (and answers). Next $n$ lines each contain one question and one answer to it. The format of each line is like that: "sign x answer", where the sign is:
- ">" (for the first type queries),
- "<" (for the second type queries),
- ">=" (for the third type queries),
- "<=" (for the fourth type queries).
All values of $x$ are integer and meet the inequation $-10^{9}<=x<=10^{9}$ . The answer is an English letter "Y" (for "yes") or "N" (for "no").
Consequtive elements in lines are separated by a single space.
- ">" (for the first type queries),
- "<" (for the second type queries),
- ">=" (for the third type queries),
- "<=" (for the fourth type queries).
All values of $x$ are integer and meet the inequation $-10^{9}<=x<=10^{9}$ . The answer is an English letter "Y" (for "yes") or "N" (for "no").
Consequtive elements in lines are separated by a single space.
输出格式
Print any of such integers $y$ , that the answers to all the queries are correct. The printed number $y$ must meet the inequation $-2·10^{9}<=y<=2·10^{9}$ . If there are many answers, print any of them. If such value doesn't exist, print word "Impossible" (without the quotes).
输入输出样例
输入 #1
4 >= 1 Y < 3 N <= -3 N > 55 N
输出 #1
17
输入 #2
2 > 100 Y < -100 Y
输出 #2
Impossible