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.Generic;
using System.Diagnostics;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Numerics;
using System.Reflection.Emit;
using System.Runtime.InteropServices;
using System.Text;
using static System.Console;
using static System.Math;

//using CS_Contest.Graph;
using CS_Contest.Loop;
using CS_Contest.Utils;
using static Nakov.IO.Cin;
using static CS_Contest.IO.IO;
using static CS_Contest.Utils.MyMath;


namespace CS_Contest {
    using bint = BigInteger;
    using Li = List<int>;
    using LLi = List<List<int>>;
    using Ll = List<long>;
    using ti3 = Tuple<int, int, int>;
    using ti2 = Tuple<int, int>;
    using tl3 = Tuple<long, long, long>;
    internal class Program {
        private static void Main(string[] args) {
            var sw = new StreamWriter(OpenStandardOutput()) { AutoFlush = false };
            SetOut(sw);
            new Calc().Solve();
            Out.Flush();
        }

        public class Calc {
            public void Solve() {
                int A = NextInt(), B = NextInt();
                (B*A-B-A+1).WL();
            }

        }
    }
}
namespace Nakov.IO {
    using System;
    using System.Text;
    using System.Globalization;

    public static class Cin {
        public static string NextToken() {
            var tokenChars = new StringBuilder();
            var tokenFinished = false;
            var skipWhiteSpaceMode = true;
            while (!tokenFinished) {
                var nextChar = Read();
                if (nextChar == -1) {
                    tokenFinished = true;
                }
                else {
                    var ch = (char)nextChar;
                    if (char.IsWhiteSpace(ch)) {
                        if (skipWhiteSpaceMode) continue;
                        tokenFinished = true;
                        if (ch == '\r' && (Environment.NewLine == "\r\n")) {
                            Read();
                        }
                    }
                    else {
                        skipWhiteSpaceMode = false;
                        tokenChars.Append(ch);
                    }
                }
            }

            var token = tokenChars.ToString();
            return token;
        }

        public static int NextInt() {
            var token = NextToken();
            return int.Parse(token);
        }
        public static long NextLong() {
            var token = NextToken();
            return long.Parse(token);
        }
        public static double NextDouble(bool acceptAnyDecimalSeparator = true) {
            var token = NextToken();
            if (acceptAnyDecimalSeparator) {
                token = token.Replace(',', '.');
                var result = double.Parse(token, CultureInfo.InvariantCulture);
                return result;
            }
            else {
                var result = double.Parse(token);
                return result;
            }
        }
        public static decimal NextDecimal(bool acceptAnyDecimalSeparator = true) {
            var token = NextToken();
            if (acceptAnyDecimalSeparator) {
                token = token.Replace(',', '.');
                var result = decimal.Parse(token, CultureInfo.InvariantCulture);
                return result;
            }
            else {
                var result = decimal.Parse(token);
                return result;
            }
        }

        public static BigInteger NextBigInteger(bool acceptAnyDecimalSeparator = true) {
            var token = NextToken();
            if (!acceptAnyDecimalSeparator) return BigInteger.Parse(token);
            token = token.Replace(',', '.');
            return BigInteger.Parse(token, CultureInfo.InvariantCulture);
        }

    }
}

namespace CS_Contest.Loop {
    [DebuggerStepThrough]
    public static class Loop {
        public static void REP(this int n, Action<int> act) {
            for (var i = 0; i < n; i++) {
                act(i);
            }
        }

        public static void ForeachWith<T>(this IEnumerable<T> ie, Action<int, T> act) {
            var i = 0;
            foreach (var item in ie) {
                act(i, item);
                i++;
            }
        }

        public static void Foreach<T>(this IEnumerable<T> ie, Action<T> act) {
            foreach (var item in ie) {
                act(item);
            }
        }

    }

    public class Generate {
        public static IEnumerable<int> Seq(int e) => Seq(0, e, 1);
        public static IEnumerable<int> Seq(int s, int e) => Seq(s, e, 1);
        public static IEnumerable<int> Seq(int s, int e, int a) {
            while (s != e) {
                yield return s;
                s += a;
            }
        }
        public static List<T> Repeat<T>(Func<int, T> result, int range) =>
            Enumerable.Range(0, range).Select(result).ToList();
    }
}

namespace CS_Contest.IO {
    using Li = List<int>;
    using Ll = List<long>;

    public static class IO {
        public static void WL(this object obj) => WriteLine(obj);
        public static void WL(this string obj) => WriteLine(obj);
        public static void WL<T>(this IEnumerable<T> list) => list.ToList().ForEach(x => x.WL());

        public static Li NextIntList() => ReadLine().Split().Select(int.Parse).ToList();
        public static Li NextIntList(int n) => Enumerable.Repeat(0, n).Select(x => ReadLine()).Select(int.Parse).ToList();
        public static Ll NextLongList() => ReadLine().Split().Select(long.Parse).ToList();

        public static T Tee<T>(this T t, Func<T, string> formatter = null) {
            if (formatter == null) formatter = arg => arg.ToString();
            formatter(t).WL();
            return t;
        }
        public static void JoinWL<T>(this IEnumerable<T> @this, string sp = " ") => @this.StringJoin(sp).WL();
        public static void W(this object @this) => Write(@this);

        public static T[,] GetBox<T>(int h, int w, Func<int, int, T> getFunc) {
            var rt = new T[h, w];
            for (var i = 0; i < h; i++) {
                for (var j = 0; j < w; j++) {
                    rt[i, j] = getFunc(i, j);
                }
            }

            return rt;
        }

    }


}

namespace CS_Contest.Utils {
    using Li = List<int>;
    using Ll = List<long>;
    using bint = BigInteger;

    [DebuggerStepThrough]
    public static class Utils {
        public static bool AnyOf<T>(this T @this, params T[] these) where T : IComparable {
            return these.Contains(@this);
        }

        public static bool Within(int x, int y, int lx, int ly) => !(x < 0 || x >= lx || y < 0 || y >= ly);

        public static void Add<T1, T2>(this List<Tuple<T1, T2>> list, T1 t1, T2 t2) =>
            list.Add(new Tuple<T1, T2>(t1, t2));

        public static string StringJoin<T>(this IEnumerable<T> l, string separator = "") => string.Join(separator, l);

        public static Queue<T> ToQueue<T>(this IEnumerable<T> iEnumerable) {
            var rt = new Queue<T>();
            foreach (var item in iEnumerable) {
                rt.Enqueue(item);
            }

            return rt;
        }

        public static void Swap<T>(ref T x, ref T y) {
            var tmp = x;
            x = y;
            y = tmp;
        }

        public static List<Tuple<TKey, TValue>> ToTupleList<TKey, TValue>(this Map<TKey, TValue> @this) =>
            @this.Select(x => Tuple.Create(x.Key, x.Value)).ToList();


        public static Map<TKey, int> CountUp<TKey>(this IEnumerable<TKey> l) {
            var dic = new Map<TKey, int>();
            foreach (var item in l) {
                dic[item]++;
            }

            return dic;
        }

        public static int Count<T>(this IEnumerable<T> l, T target) => l.Count(x => x.Equals(target));

        public static IEnumerable<T> SkipAt<T>(this IEnumerable<T> @this, int at) {
            var enumerable = @this as T[] ?? @this.ToArray();
            for (var i = 0; i < enumerable.Count(); i++) {
                if (i == at) continue;
                yield return enumerable.ElementAt(i);
            }
        }

        public static int LowerBound<T>(this List<T> @this, T x) where T : IComparable {
            int lb = -1, ub = @this.Count;
            while (ub - lb > 1) {
                var mid = (ub + lb) >> 1;
                if (@this[mid].CompareTo(x) >= 0) ub = mid;
                else lb = mid;
            }

            return ub;
        }

        public static int UpperBound<T>(this List<T> @this, T x) where T : IComparable {
            int lb = -1, ub = @this.Count;
            while (ub - lb > 1) {
                var mid = (ub + lb) >> 1;
                if (@this[mid].CompareTo(x) > 0) ub = mid;
                else lb = mid;
            }

            return ub;
        }

        public static List<int> Imos(this IEnumerable<int> @this) {
            var rt = @this.ToList();
            for (var i = 0; i < rt.Count - 1; i++) rt[i + 1] += rt[i];
            return rt;
        }

        public static List<long> Imos(this IEnumerable<long> @this) {
            var rt = @this.ToList();
            for (var i = 0; i < rt.Count - 1; i++) rt[i + 1] += rt[i];
            return rt;
        }

        public static bool IsOdd(this long @this) => @this % 2 == 1;
        public static bool IsOdd(this int @this) => @this % 2 == 1;
        public static bool IsOdd(this bint @this) => @this % 2 == 1;

    }



    public class Map<TKey, TValue> : Dictionary<TKey, TValue> {
        public Map() : base() { }
        public Map(int capacity) : base(capacity) { }

        public new TValue this[TKey index] {
            get {
                TValue v;
                return TryGetValue(index, out v) ? v : base[index] = default(TValue);
            }
            set { base[index] = value; }
        }
    }

    public static class MyMath {

        public static T EMin<T>(params T[] a) where T : IComparable<T> => a.Min();
        public static T EMax<T>(params T[] a) where T : IComparable<T> => a.Max();

    }


}