use std::env;
use std::fs::File;
use std::io::{BufRead, BufReader};

fn main() {
    let reader = open_file();

    let mut points: Vec<Vec<u32>> = Vec::new();

    for line in reader.lines() {
        points.push(
            line.unwrap()
                .trim()
                .chars()
                .map(|x| x.to_digit(10).unwrap())
                .collect(),
        );
    }

    let nine = vec![9];

    let mut risk_level: u32 = 0;

    for (idx, height) in points.iter().enumerate() {
        for (ndx, num) in height.iter().enumerate() {
            let up = points
                .get(((idx as isize) - 1) as usize)
                .unwrap_or_else(|| &nine)
                .get(ndx)
                .unwrap_or_else(|| &9);

            let down = match points.get(idx + 1) {
                Some(line) => match line.get(ndx) {
                    Some(number) => number,
                    None => &9,
                },
                None => &9,
            };
            let left = match height.get((ndx as isize - 1) as usize) {
                Some(number) => number,
                None => &9,
            };
            let right = match height.get(ndx + 1) {
                Some(number) => number,
                None => &9,
            };
            if num < up && num < down && num < right && num < left {
                risk_level += 1 + *num;
            }
        }
    }
    println!("{}", risk_level);
}

fn open_file() -> BufReader<File> {
    let args: Vec<String> = env::args().collect();

    if args.len() != 2 {
        eprintln!("Usage: {} <filename>", args[0]);
        std::process::exit(1);
    }

    let filename = &args[1];

    let file = File::open(filename).unwrap_or_else(|_| panic!("No such file: {}", filename));
    BufReader::new(file)
}