use std::io::{self, Read};


fn process_one(mut data: Vec<i64>) -> usize {
    let mut index: i64 = 0;
    let mut steps = 0;

    loop {
        let addr = data[index as usize];

        data[index as usize] += 1;

        index += addr;
        steps += 1;

        if index < 0 || index as usize >= data.len() {
            break;
        }
    }

    steps
}

fn process_two(mut data: Vec<i64>) -> usize {
    let mut index: i64 = 0;
    let mut steps = 0;

    loop {
        if index < 0 || index as usize >= data.len() {
            break;
        }

        let addr = data[index as usize];

        data[index as usize] += if addr < 3 { 1 } else { -1 };

        index += addr;
        steps += 1;
    }

    steps
}

fn parse(input: &str) -> Vec<i64> {
    input.lines().filter_map(|line| line.parse().ok()).collect()
}


fn main() {
    let mut input = String::new();

    io::stdin()
        .read_to_string(&mut input)
        .expect("faild to read input");

    let data = parse(&input);

    println!("part_one={}", process_one(data.clone()));
    println!("part_two={}", process_two(data));
}


#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_parse() {
        let input = "0\n\
                     3\n\
                     0\n\
                     1\n\
                     -3";

        assert_eq!(parse(input), vec![0, 3, 0, 1, -3]);
    }

    #[test]
    fn test_process_one() {
        assert_eq!(process_one(vec![0, 3, 0, 1, -3]), 5);
    }

    #[test]
    fn test_process_two() {
        assert_eq!(process_two(vec![0, 3, 0, 1, -3]), 10);
    }
}