using System;
using System.Linq;
using System.Collections.Generic;

namespace Contest
{
  class Program
  {
    static void Main(string[] args)
    {
      ABC165.D();
    }
    class ABC165
    {
      public static void A()
      {
        var K = Read.Int();
        var A = Read.Int();
        var B = Read.Int();
        for(int i = A; i <= B; ++i)
        {
          if (i % K == 0)
          {
            Console.WriteLine("OK");
            return;
          }
        }
        Console.WriteLine("NG");
      }
      public static void B()
      {
        var X = Read.Long();
        long current = 100;
        int count = 0;
        while (current < X)
        {
          current += current / 100;
          count++;
        }
        Console.WriteLine(count);
      }
      public static void C()
      {
        var N = Read.Int();
        var M = Read.Int();
        var Q = Read.Int();
        var ABCD = Enumerable.Range(0, Q).Select(i => Read.IntN()).ToArray();
        var A = new int[N];
        A[0] = 1;
        Console.WriteLine(C_DFS(A, 1, N, M, ABCD, 0));
      }
      static int C_DFS(int[] A, int depth, int N, int M, int[][] ABCD, int score)
      {
        if (depth == N)
        {
          int sum = 0;
          for (int i = 0; i < ABCD.Length; ++i)
          {
            var abcd = ABCD[i];
            if (A[abcd[1] - 1] - A[abcd[0] - 1] == abcd[2]) { sum += abcd[3]; }
          }
          return sum;
        }
        else
        {
          int res = score;
          for (int i = A[depth - 1]; i <= M; ++i)
          {
            A[depth] = i;
            res = Math.Max(res, C_DFS(A, depth + 1, N, M, ABCD, score));
          }
          return res;
        }
      }
      public static void D()
      {
        var A = Read.Long();
        var B = Read.Long();
        var N = Read.Long();
        var X = Math.Min(B - 1, N);
        Console.WriteLine(A * X / B - X / B * A);
      }
      public static void E()
      {

      }
      public static void F()
      {

      }
    }
    class Util
    {
      public static readonly long P = 1000000007;
      public static long[] ASum(long[] array)
      {
        var res = new long[array.Length + 1];
        for (int i = 0; i < array.Length; ++i)
        {
          res[i + 1] = res[i] + array[i];
        }
        return res;
      }
      public static Dictionary<T, long> Frequency<T>(T[] array)
      {
        var dict = new Dictionary<T, long>();
        foreach (var a in array)
        {
          if (!dict.ContainsKey(a)) { dict.Add(a, 0); }
          dict[a]++;
        }
        return dict;
      }
    }


    static class Read
{
static Queue<string> queue = new Queue<string>();
static void Enqueue() { var ss = Console.ReadLine().Split(' '); foreach (var s in ss) { queue.Enqueue(s); } }
public static int Int() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt32(queue.Dequeue()); }
public static long Long() { if (queue.Count == 0) { Enqueue(); } return Convert.ToInt64(queue.Dequeue()); }
public static string Str() { if (queue.Count == 0) { Enqueue(); } return queue.Dequeue(); }
public static int[] IntN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt32(s)).ToArray(); }
public static long[] LongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToInt64(s)).ToArray(); }
public static ulong[] ULongN() { return Console.ReadLine().Split(' ').Select(s => Convert.ToUInt64(s)).ToArray(); }
public static string[] StrN() { return Console.ReadLine().Split(' '); }
public static Tuple<int, int>[] TupleInt(int n) { List<Tuple<int, int>> list = new List<Tuple<int, int>>(); for (int i = 0; i < n; ++i) { var ab = Read.IntN(); list.Add(new Tuple<int, int>(ab[0], ab[1])); } return list.ToArray(); }
public static Tuple<long, long>[] TupleLong(int n) { List<Tuple<long, long>> list = new List<Tuple<long, long>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<long, long>(ab[0], ab[1])); } return list.ToArray(); }
public static Tuple<string, string>[] TupleStr(int n) { List<Tuple<string, string>> list = new List<Tuple<string, string>>(); for (int i = 0; i < n; ++i) { var ab = Read.StrN(); list.Add(new Tuple<string, string>(ab[0], ab[1])); } return list.ToArray(); }
public static Tuple<double, double>[] TupleDouble(int n) { List<Tuple<double, double>> list = new List<Tuple<double, double>>(); for (int i = 0; i < n; ++i) { var ab = Read.LongN(); list.Add(new Tuple<double, double>(ab[0], ab[1])); } return list.ToArray(); }
public static long[,] LongMatrix(int r, int c) { var mat = new long[r, c]; for (int i = 0; i < r; ++i) { var x = Read.LongN(); for (int j = 0; j < c; ++j) { mat[i, j] = x[j]; } } return mat; }
public static Dictionary<int, HashSet<int>> AdjacencyList(int N, int M, bool isDirectional = false)
{
Dictionary<int, HashSet<int>> dict = new Dictionary<int, HashSet<int>>();
for (int i = 0; i <= N; ++i) { dict.Add(i, new HashSet<int>()); }
for (int i = 0; i < M; ++i) { var ab = Read.IntN(); dict[ab[0]].Add(ab[1]); if (!isDirectional) { dict[ab[1]].Add(ab[0]); } }
return dict;
}
public static Dictionary<int, Dictionary<int, long>> AdjacencyListWithWeight(int N, int M)
{
Dictionary<int, Dictionary<int, long>> dict = new Dictionary<int, Dictionary<int, long>>(); for (int i = 0; i <= N; ++i) { dict.Add(i, new Dictionary<int, long>()); }
for (int i = 0; i < M; ++i) { var ab = Read.IntN(); dict[ab[0]].Add(ab[1], ab[2]); dict[ab[1]].Add(ab[0], ab[2]); }
return dict;
}
}
    }
}


Measured memory_bytes: 17976