Problem:
﻿Score: 100 points

Problem Statement

There is a farm whose length and width are A yard and B yard, respectively. A farmer, John, made a vertical road and a horizontal road inside the farm from one border to another, as shown below: (The gray part represents the roads.)

What is the area of this yard excluding the roads? Find it.

Note

It can be proved that the positions of the roads do not affect the area.

Constraints

A is an integer between 2 and 100 (inclusive).

B is an integer between 2 and 100 (inclusive).

Input

Input is given from Standard Input in the following format:

A B

Output

Print the area of this yard excluding the roads (in square yards).

Sample Input 1

2 2

Sample Output 1

1

In this case, the area is 1 square yard.

Sample Input 2

5 7

Sample Output 2

24

In this case, the area is 24 square yards.

Solution in Rust (1.15.1) (judge verdict: Accepted)

trait FromFragment: Sized {
    fn from_fragment(s: &str) -> Result<Self, String>;
}

impl FromFragment for String {
    fn from_fragment(s: &str) -> Result<String, String> { Ok(s.to_owned()) }
}

#[allow(unused_macros)]
macro_rules! impl_from_fragment {
    ( $( $t:ty )* ) => { $(
        impl FromFragment for $t {
            fn from_fragment(s: &str) -> Result<$t, String> {
                use std::str::FromStr;
                <$t>::from_str(s).map_err(|_| {
                    format!("cannot parse \"{}\" as {}", s, stringify!($t))
                })
            }
        }
    )* };
}

impl_from_fragment!(isize usize i8 u8 i16 u16 i32 u32 i64 u64 f64);

#[test]
fn test_from_fragemnt() {
    assert_eq!(i32::from_fragment("42"), Ok(42));
    assert_eq!(String::from_fragment("string"), Ok("string".to_owned()));
}

trait FromLine: Sized {
    fn from_line(line: &str) -> Result<Self, String>;
}

impl<T: FromFragment> FromLine for T {
    fn from_line(line: &str) -> Result<T, String> {
        T::from_fragment(line.trim_right_matches('\n'))
    }
}

impl<T: FromFragment> FromLine for Vec<T> {
    fn from_line(line: &str) -> Result<Vec<T>, String> {
        let mut result = Vec::new();
        for fragment in line.trim_right_matches('\n').split_whitespace() {
            match T::from_fragment(fragment) {
                Ok(v) => result.push(v),
                Err(msg) => {
                    return Err(format!(
                        "fragment {} of line \"{}\": {}",
                        result.len() + 1, line, msg
                    ))
                }
            }
        }
        Ok(result)
    }
}

#[allow(unused_macros)]
macro_rules! impl_from_line_for_tuples {
    ($t:ident $var:ident $count:expr) => ();
    ($t:ident $var:ident $count:expr; $($inner_t:ident $inner_var:ident $inner_count:expr);*) => {
        impl <$t: FromFragment, $($inner_t: FromFragment),*> FromLine for ($t, $($inner_t),*) {
            #[allow(unused_assignments)]
            fn from_line(line: &str) -> Result<( $t, $($inner_t),*), String> {
                let fragments: Vec<&str> =
                    line.trim_right_matches('\n').split_whitespace().collect();
                if fragments.len() != $count {
                    return Err(format!(
                        "line \"{}\" has {} fragments, expected {}",
                        line, fragments.len(), $count
                    ));
                }

                let mut iter = fragments.iter();
                let mut n = 1;
                let $var = <$t>::from_fragment(iter.next().unwrap())
                    .map_err(|msg| {
                        format!("fragment {} of line \"{}\": {}", n, line, msg)
                    })?;
                n += 1;
                $(
                    let $inner_var =
                        <$inner_t>::from_fragment(iter.next().unwrap())
                        .map_err(|msg| {
                            format!("fragment {} of line \"{}\": {}",
                                    n, line, msg)
                        })?;
                    n += 1;
                )*
                Ok(( $var, $($inner_var),* ))
            }
        }
        impl_from_line_for_tuples!($($inner_t $inner_var $inner_count);*);
    }
}

impl_from_line_for_tuples!(T4 x4 4; T3 x3 3; T2 x2 2; T1 x1 1);

#[allow(unused_macros)]
macro_rules! read {
    // Discard a line
    () => {
        let mut line = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
    };

    // Get a FromLine
    ( $pat:pat = $t:ty ) => {
        let mut line = String::new();
        std::io::stdin().read_line(&mut line).unwrap();
        let $pat = <$t>::from_line(&line).unwrap();
    };

    // Get FromFragment's
    ( $( $pat:pat = $t:ty ),+ ) => {
        read!(($($pat),*) = ($($t),*));
    };
}

#[allow(unused_macros)]
macro_rules! read_n {
    // Get FromLine's
    ( $( $pat:pat = $t:ty ),+ ) => {
        $(
            read!($pat = $t);
        )*
    }
}

#[allow(unused_macros)]
macro_rules! read_loop {
    ( $pat:pat = $t:ty; $block:block ) => {
        use std::io::BufRead;
        let stdin = std::io::stdin();
        for line in stdin.lock().lines() {
            let line = line.expect("read from stdin failed");
            let $pat = <$t>::from_line(&line).unwrap();
            $block
        }
    };

    ( $($pat:pat = $t:ty),* ; $block:block ) => {
        read_loop!(($($pat),*) = ($($t),*); $block);
    }
}

fn main() {
    read!(a = u32, b = u32);
    println!("{}", (a-1) * (b-1));
}