fn main() {
	for io::stdin().each_line() |line| {
		let mut total = 0.0;
		let mut count = 0.0;
		let pivot=line.char_at(0);
		for str::each_char(line.slice(2, line.char_len())) |c| {
			total += 1.0;
			if c == pivot {
				count += 1.0;
			};
		};
		io::println(fmt!("%0.6f", count/total));
	}
}