fibo

use std::io;
use std::f32;

fn main() {

    const FIBO_CONST: f32 = 1.618034;
    let five:f32 = 5_f32.sqrt();

    println!("input Fibo number");
    let mut index = String::new();

    io::stdin()
        .read_line(&mut index)
        .expect("fail");

    let index: u8 = index.trim().parse().expect("please write a number");

    if index > 0 {

        let number = (FIBO_CONST.powf(index.into()) - (1.0 - FIBO_CONST).powf(index.into()))/five;
        let result = number as i32;
        println!("your fibo is: {}", result);

    } else{

        println!("input Fibo number");
        let mut index = String::new();

        io::stdin()
            .read_line(&mut index)
            .expect("fail");

        let _index: u8 = index.trim().parse().expect("please write a number");
    };
}