Code shared from the Rust Playground

playground.rs

extern crate num;
use num::bigint::BigInt;

fn main() {

    match "123123123123123123123".parse::<BigInt>() {
        Ok(n)  => println!("{}", n),
        Err(_) => println!("Error")
    }
    
    let bytes = "ff".as_bytes();
    let i = BigInt::parse_bytes(bytes, 16).unwrap();
    println!("{}", i);
}