Replace Character in a String

You are given a string s and two characters: old_char and new_char. Your task is to replace every occurrence of old_char in s with new_char. The replacement should be case-sensitive, meaning that only the characters that exactly match old_char (including their case) should be replaced.

For example, if s is "hello world", old_char is 'l' and new_char is 'x', then the output should be "hexxo worxd". If new_char is an empty string, then all occurrences of old_char should be removed.

Note: If old_char does not occur in s, simply print the original string.

You can represent the character replacement function mathematically as follows:

$$ f(s, c, d) = \text{replace}(s, c, d) $$

where \( \text{replace}(s, c, d) \) returns a new string in which every occurrence of character \( c \) in \( s \) is replaced by character \( d \).

inputFormat

The input is read from stdin and consists of three lines:

1. The first line contains the string s.
2. The second line contains the character old_char to be replaced.
3. The third line contains the character new_char which will replace old_char. This line could be empty indicating that old_char should be removed.

outputFormat

Output to stdout a single line containing the modified string after all replacements.

## sample

hello world
l
x

hexxo worxd