fn main() {
println!("fib(1) = {}", fib(1));
println!("fib(7) = {}", fib(7));
println!("fib(19) = {}", fib(19));
}
fn fib(i: u64) -> u64 {
let mut a = 0;
let mut b = 1;
for _ in 0..i {
(a, b) = (b, a + b);
a
