using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.Linq;
using System.Numerics;

namespace AtCoderWorkspace
{
    public class Solver
    {
        public void Solve()
        {
            var cin = new Scanner();

            var a = (double)cin.nextLong();
            var b = (double)cin.nextLong();
            var n = cin.nextLong();

            var x = Math.Min(n, b - 1);

            Console.WriteLine(Math.Floor((a * x) / b) - (a * Math.Floor(x / b)));
        }
    }

    class NBinarySearch
    {
        long ok;
        long ng;
        Func<long, bool> isOK;

        /// <param name="ok">必ず条件を満たすN</param>
        /// <param name="ng">必ず条件を満たさないN</param>
        /// <param name="isOK">midの判定</param>
        public NBinarySearch(long ok, long ng, Func<long, bool> isOK)
        {
            this.ok = ok;
            this.ng = ng;
            this.isOK = isOK;
        }

        public long OK()
        {
            long ok = this.ok;
            long ng = this.ng;

            while (Math.Abs(ok - ng) > 1)
            {
                long mid = (ok + ng) / 2;

                if (isOK(mid)) ok = mid;
                else ng = mid;
            }
            return ok;
        }

        public long NG()
        {
            long ok = this.ok;
            long ng = this.ng;

            while (Math.Abs(ok - ng) > 1)
            {
                long mid = (ok + ng) / 2;

                if (isOK(mid)) ok = mid;
                else ng = mid;
            }
            return ng;
        }
    }

    class Scanner
    {
        string[] s;
        int i;

        char[] cs = new char[] { ' ' };

        public Scanner()
        {
            s = new string[0];
            i = 0;
        }

        public string next()
        {
            if (i < s.Length) return s[i++];
            string st = Console.ReadLine();
            while (st == "") st = Console.ReadLine();
            s = st.Split(cs, StringSplitOptions.RemoveEmptyEntries);
            if (s.Length == 0) return next();
            i = 0;
            return s[i++];
        }

        public int nextInt()
        {
            return int.Parse(next());
        }
        public int[] ArrayInt(int N, int add = 0)
        {
            int[] Array = new int[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextInt() + add;
            }
            return Array;
        }

        public int[] DPArrayInt(int N, int ex)
        {
            int[] Array = new int[N + ex];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextInt();
            }
            return Array;
        }

        public long nextLong()
        {
            return long.Parse(next());
        }

        public long[] ArrayLong(int N, long add = 0)
        {
            long[] Array = new long[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextLong() + add;
            }
            return Array;
        }

        public long[] DPArrayLong(int N, int ex)
        {
            long[] Array = new long[N + ex];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextLong();
            }
            return Array;
        }

        public double nextDouble()
        {
            return double.Parse(next());
        }


        public double[] ArrayDouble(int N, double add = 0)
        {
            double[] Array = new double[N];
            for (int i = 0; i < N; i++)
            {
                Array[i] = nextDouble() + add;
            }
            return Array;
        }
    }

    class Program
    {
        static void Main(string[] s) => new Solver().Solve();
    }
}

Measured memory_bytes: 27408