- Time limit: 1.00 s
- Memory limit: 512 MB
Each family member gives two wishes concerning the toppings of the pizza. The wishes are of the form "topping $x$ is good/bad". Your task is to choose the toppings so that at least one wish from everybody becomes true (a good topping is included in the pizza or a bad topping is not included).
The first input line has two integers $n$ and $m$: the number of family members and toppings. The toppings are numbered $1,2,\dots,m$.
After this, there are $n$ lines describing the wishes. Each line has two wishes of the form "+ $x$" (topping $x$ is good) or "- $x$" (topping $x$ is bad).
Print a line with $m$ symbols: for each topping "+" if it is included and "-" if it is not included. You can print any valid solution.
If there are no valid solutions, print "IMPOSSIBLE".
- $1 \le n,m \le 10^5$
- $1 \le x \le m$
+ 1 + 2
- 1 + 3
+ 4 - 2
- + + + -