Create a function that takes a string as an argument and returns true if each letter in the string is surrounded by a plus sign. Return false otherwise.

Examples

plus_sign("+f+d+c+#+f+") ➞ true

plus_sign("+d+=3=+s+") ➞ true

plus_sign("f++d+g+8+") ➞ false

plus_sign("+s+7+fg+r+8+") ➞ false

Notes

For clarity, each letter must have a plus sign on both sides.