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 C# (Mono 4.6.2.0) (judge verdict: Accepted)

using System;
using System.Collections;
using System.Collections.Generic;
using System.Runtime.CompilerServices;
using System.IO;
using System.Linq;
using System.Runtime.InteropServices;
using System.Runtime.Remoting.Messaging;
using System.Security.Cryptography.X509Certificates;
using System.Security.Permissions;
using System.Text;
using static System.Console;
using static System.Math;
using static Ex;
class AC{
    /*------------------------------------------------------------------*/
    private int A, B;
    void Solve(){
        io.i(out A,out B);
        ((A-1)*(B-1)).Prt();
    }
    /*------------------------------------------------------------------*/
    void Test(){
        //--- TEST ---//
    }
    public static void Main(string[] args) => new AC().Stream();
    IO io = new IO();
    private void Stream(){
        /*
        var exStdIn = new System.IO.StreamReader("stdin.txt");
        SetIn(exStdIn);
        Test();
        */
        Solve();
        io.Flush();
    }
}
class IO{
    #region INPUT
    #region FastRead    
    private const int Size = 1 << 12;
    private readonly Stream _stream = OpenStandardInput();
    private readonly byte[] _buffer = new byte[Size];
    private int _ptr = 0, _buffLen = 0;
    private bool HasNextByte(){
        if(_ptr < _buffLen) return true;
        _ptr = 0;
        _buffLen = _stream.Read(_buffer, 0, Size);
        return _buffLen > 0;
    }
    private byte ReadByte(){
        if(HasNextByte()) return _buffer[_ptr++];
        else
        //inputの末尾の改行がないとerror
            throw new EndOfStreamException();
    }
    private bool IsAscii(int c) => '!' <= c && c <= '~';
    private char NextChar(){
        var b = ReadByte();
        while(!IsAscii(b)) b = ReadByte();
        return (char) b;
    }
    private string Next(){
        var sb = new StringBuilder();
        for(var b = NextChar(); IsAscii(b); b = (char) ReadByte()) sb.Append(b);
        return sb.ToString();
    }
    public string String => Next();
    public char Char => NextChar();
    public int Int => int.Parse(Next());
    public long Long => long.Parse(Next());
    public double Double => double.Parse(Next());
    #endregion
    #region LazyRead        
    private void scan<T>(ref T x){
        if(x is int) __refvalue(__makeref(x),int) = int.Parse(Next());
        else if(x is long) __refvalue(__makeref(x),long) = long.Parse(Next());
        else if(x is double) __refvalue(__makeref(x),double) = double.Parse(Next());
        else if(x is char) __refvalue(__makeref(x),char) = NextChar();
        else __refvalue(__makeref(x),string) = Next();
    }
    public void i<T>(out T t){
        t = default(T);
        scan(ref t);
    }
    public void i<T, TU>(out T t, out TU u){
        i(out t);
        i(out u);
    }
    public void i<T, TU, TV>(out T t, out TU u, out TV v){
        i(out t, out u);
        i(out v);
    }
    public void i<T, TU, TV, TW>(out T t, out TU u, out TV v, out TW w){
        i(out t, out u);
        i(out v, out w);
    }
    public void i<T, TU, TV, TW, TX>(out T t, out TU u, out TV v, out TW w, out TX x){
        i(out t, out u, out v);
        i(out w, out x);
    }
    public void i<T, TU, TV, TW, TX, TY>(out T t, out TU u, out TV v, out TW w, out TX x, out TY y){
        i(out t, out u, out v);
        i(out w, out x, out y);
    }
    public void ini<T>(out T[] a, int n){
        a = new T[n];
        for(int i = 0; i < n; ++i) i<T>(out a[i]);
    }
    public void ini<T, TU>(out T[] a, out TU[] b, int n){
        a = new T[n];
        b = new TU[n];
        for(int i = 0; i < n; ++i) i<T, TU>(out a[i], out b[i]);
    }
    public void ini<T, TU, TV>(out T[] a, out TU[] b, out TV[] c, int n){
        a = new T[n];
        b = new TU[n];
        c = new TV[n];
        for(var i = 0; i < n; ++i) i<T, TU, TV>(out a[i], out b[i], out c[i]);
    }
    public void ini<T>(out T[,] a, int h, int w){
        a = new T[h, w];
        for(int i = 0; i < h; ++i) for(int j = 0; j < w; ++j) i<T>(out a[i, j]);
    }
    #endregion
    #endregion
    #region OUTPUT
    private readonly StreamWriter _sw = new StreamWriter(OpenStandardOutput()){
#if DEBUG
        AutoFlush = true
#else
        AutoFlush = false
#endif
    };
    public void Flush() => Out.Flush();
    public void YN(bool f) => yn(f, "YES", "NO");
    public void Yn(bool f) => yn(f, "Yes", "No");
    public void yn(bool f, string y = "yes", string n = "no") => WriteLine(f ? y : n);
    #endregion
    public IO() { SetOut(_sw); }
}
static class Ex{
    #region マクロもどき      
    public static Dictionary<T1, T2> MERGE<T1, T2>(Dictionary<T1, T2> xs, Dictionary<T1, T2> ys) => xs.Except(xs.Join(ys, z => z.Key, z => z.Key, (a, b) => a)).Concat(ys).ToDictionary(z => z.Key, z => z.Value);
    public static void LOG<T>(T x, [CallerLineNumber] int line = 0) => Error.WriteLine($"--- LOG[{line}]: {x} ---");
    public static void FOR(int a, int b, Action<int> f) => FOR(a, b, 1, f);
    public static void FOR(int a, int b, int n, Action<int> f){
        for(int i = a; i < b; i += n) f(i);
    }
    public static void REP(int a, Action<int> f) => FOR(0, a, f);
    public static void REPEQ(int a, Action<int> f) => FOR(0, a + 1, f);
    public static void FOREQ(int a, int b, Action<int> f) => FOR(a, b + 1, f);
    public static void FOREQ(int a, int b, int n, Action<int> f) => FOR(a, b + 1, n, f);
    public static void REP(int a, int b, Action<int, int> f) => REP(a, i => REP(b, j => f(i, j)));
    public static void REP(int a, int b, int c, Action<int, int, int> f) => REP(a, i => REP(b, j => REP(c, k => f(i, j, k))));
    public static void REPEQ(int a, int b, Action<int, int> f) => REPEQ(a, i => REPEQ(b, j => f(i, j)));
    public static void REPEQ(int a, int b, int c, Action<int, int, int> f) => REPEQ(a, i => REPEQ(b, j => REPEQ(c, k => f(i, j, k))));
    public static T MIN<T>(params T[] xs) => xs.Min();
    public static T MAX<T>(params T[] xs) => xs.Max();
    public static IEnumerable<int> RANGE(int s, int e) => Enumerable.Range(s, e - s + 1);
    public static int LCM(int a, int b) => a * (b / GCD(a, b));
    public static int GCD(int a, int b) => (a < b) ? GCD(b, a) : b == 0 ? a : GCD(b, a % b);
    public static int LCM(params int[] xs) => xs.Aggregate(LCM);
    public static int GCD(params int[] xs) => xs.Aggregate(GCD);
    public static long LCM(long a, long b) => a * (b / GCD(a, b));
    public static long GCD(long a, long b) => (a < b) ? GCD(b, a) : b == 0L ? a : GCD(b, a % b);
    public static long LCM(params long[] xs) => xs.Aggregate(LCM);
    public static long GCD(params long[] xs) => xs.Aggregate(GCD);
    #endregion
    #region 拡張メソッド        
    public static void Rep(this int x, Action<int> f) => REP(x, f);
    public static void RepEq(this int x, Action<int> f) => REPEQ(x, f);
    public static int ToInt(this string s){
        double n;
        double.TryParse(s.TrimStart('0'), out n);
        return Convert.ToInt32(n);
    }
    public static int ToInt(this char c) => ToInt(c.ToString());
    public static int ToInt(this char[] c) => ToInt(new string(c));
    public static long ToLong(this string s){
        double n;
        double.TryParse(s.TrimStart('0'), out n);
        return Convert.ToInt64(n);
    }
    public static long ToLong(this int x) => (long) x;
    public static IEnumerable<long> ToLong(this IEnumerable<int> xs) => xs.Select(x => x.ToLong());
    public static long ToLong(this char c) => ToLong(c.ToString());
    public static long ToLong(this char[] c) => ToLong(new string(c));
    public static int ToMod(this int x, int mod = (int) (1e9 + 7)) => x % mod;
    public static long ToMod(this long x, long mod = (long) (1e9 + 7)) => x % mod;
    public static void Do<T>(this T x, Action<T> f) => f(x);
    public static TU Then<T, TU>(this T x, Func<T, TU> f) => f(x);
    public static void Fun<T>(this T[] xs, Action<int> f) => REP(xs.Length, f);
    public static void Fun<T>(this T[,] xxs, Action<int, int> f) => REP(xxs.GetLength(0), i => REP(xxs.GetLength(1), j => f(i, j)));
    public static bool IsIn<T>(this T[] xs, int i) => 0 <= i && i < xs.Length;
    public static bool IsIn<T>(this T[,] xxs, int i, int j) => 0 <= i && i < xxs.GetLength(0) && 0 <= j && j < xxs.GetLength(1);
    public static void Iter<T>(this IEnumerable<T> xs, Action<T> f){
        foreach(var x in xs) f(x);
    }
    public class IndexedItem<T>{
        public int Idx;
        public T Val;
        public IndexedItem(int idx, T val){
            Idx = idx;
            Val = val;
        }
    }
    public static IEnumerable<IndexedItem<T>> Indexed<T>(this IEnumerable<T> xs) => xs.Select((x, i) => new IndexedItem<T>(i, x));
    public static Dictionary<long, int> PrimeFactor(this int x) => ((long) x).PrimeFactor();
    public static Dictionary<long, int> PrimeFactor(this long n){
        var ret = new Dictionary<long, int>();
        for(var i = 2; i <= n; ++i){
            if(!ret.ContainsKey(i)) ret[i] = 0;
            while(n % i == 0){
                ++ret[i];
                n /= i;
            }
        }
        return ret.Where(kp => kp.Value != 0).ToDictionary(kp => kp.Key, kp => kp.Value);
    }
    public static void Set<T>(this T[] xs, T v) => REP(xs.Length, i => xs[i] = v);
    public static void Set<T>(this T[,] xxs, T v) => REP(xxs.GetLength(0), i => REP(xxs.GetLength(1), j => xxs[i, j] = v));
    public static T[] Sort<T>(this T[] xs){
        Array.Sort(xs);
        return xs;
    }
    public static T[] SortR<T>(this T[] xs){
        Array.Reverse(xs.Sort());
        return xs;
    }
    public static string Pad0<T>(this T s, int n) => s.ToString().PadLeft(n, '0');
    public static int RoundOff(this double v, int n) => (int) Round(v, n - 1, MidpointRounding.AwayFromZero);
    public static int RoundUp(this double v) => (int) Ceiling(v);
    public static int RoundDown(this double v) => (int) Floor(v);
    public static bool Odd(this int v) => (v & 1) != 0;
    public static bool Odd(this long v) => (v & 1) != 0;
    public static bool Eve(this int v) => !v.Odd();
    public static bool Eve(this long v) => !v.Odd();
    public static void Prt<T>(this T x) => WriteLine(x);
    public static void Prt<T>(this T[] xs) => xs.Iter(x => WriteLine(x));
    public static void Prt<T>(this List<T> xs) => xs.Iter(x => WriteLine(x));
    public static void Prt<T>(this T[,] xs) => xs.GetLength(0).Rep(i =>{
        xs.GetLength(1).Rep(j => Write($"{xs[i, j]} "));
        WriteLine();
    });
    public static void Prt_<T>(this T[] xs) => WriteLine(string.Join(" ", xs));
    public static void Log<T>(this T x, [CallerLineNumber] int line = 0){
#if DEBUG
        Error.WriteLine($"--- LOG[{line}]: {x} ---");
#endif
    }
    public static void Log<T>(this T[] xs, [CallerLineNumber] int line = 0){
#if DEBUG
        Error.WriteLine($"^^^ LOG[{line}] ^^^");
        xs.Iter(x => Error.WriteLine(x));
        Error.WriteLine($"vvv LOG[{line}] vvv\n");
#endif
    }
    public static void Log<T>(this T[,] xs, [CallerLineNumber] int line = 0){
#if DEBUG
        Error.WriteLine($"^^^ LOG[{line}] ^^^");
        xs.GetLength(0).Rep(i =>{
            xs.GetLength(1).Rep(j => Error.Write($"{xs[i, j]} "));
            Error.WriteLine();
        });
        Error.WriteLine($"vvv LOG[{line}] vvv\n");
#endif
    }
    public static string Reversed(this string s) => string.Join("", s.Reverse());
    public static string Repeat(this string s, int n) => string.Concat(Enumerable.Repeat(s, n).ToArray());
    #endregion
}