Problem:
Score : 400 points

Problem Statement

Given are integers A, B, and N.

Find the maximum possible value of floor(Ax/B) - A × floor(x/B) for a non-negative integer x not greater than N.

Here floor(t) denotes the greatest integer not greater than the real number t.

Constraints

1 ≤ A ≤ 10^{6}

1 ≤ B ≤ 10^{12}

1 ≤ N ≤ 10^{12}

All values in input are integers.

Input

Input is given from Standard Input in the following format:

A B N

Output

Print the maximum possible value of floor(Ax/B) - A × floor(x/B) for a non-negative integer x not greater than N, as an integer.

Sample Input 1

5 7 4

Sample Output 1

2

When x=3, floor(Ax/B)-A×floor(x/B) = floor(15/7) - 5×floor(3/7) = 2. This is the maximum value possible.

Sample Input 2

11 10 9

Sample Output 2

9

Solution in Java (OpenJDK 11.0.6) (judge verdict: Accepted)

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Arrays;

public class Main {

	static BufferedReader reader;
	final static boolean MODE_DEBUG = false;
	//static field here
	
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		reader = new BufferedReader(new InputStreamReader(System.in));
		//code here
		long[] a = readLineLong();
		long A = a[0];
		long B = a[1];
		long N = a[2];
		
		long max_xB = 0;
		long max_x = 0;
		long loop_cnt = 0;
		for(long x=B-1;x<N;x+=B) {
			long calc = (A*x)/B-A*(x/B);
			if(calc>max_xB) {
				max_xB = calc;
				max_x = x;
			}
			loop_cnt++;
			if(loop_cnt<=A) {break;}
		}
		long calc = (A*N)/B-A*(N/B);
		if(calc>max_xB) {
			max_xB = calc;
			max_x = N;
		}
		print(max_xB);
	}
	
	//functions here
	//note that all methods should be STATIC


	private static <T> int arraySearch(T needle, T[] heystack) {
		for(int i=0;i<heystack.length;i++) {
			if(needle.equals(heystack[i])) {
				return i;
			}
		}
		return -1;
	}
	private static int[] sort(int[] base) {
		int[] copy = array_copy(base);
		Arrays.sort(copy);
		return copy;
	}
	private static int[] array_copy(int[] base) {
		int[] copy = new int[base.length];
		for(int i=0;i<base.length;i++) {
			copy[i] = base[i];
		}
		return copy;
	}
	private static int[] asArray(ArrayList<Integer> ints) {
		int[] intlist = new int[ints.size()];
		for(int i=0;i<intlist.length;i++) {
			intlist[i] = ints.get(i);
		}
		return intlist;
	}
	private static String[] readLine(){
		try{
			return reader.readLine().split(" ");
		}catch(Exception e){
			e.printStackTrace();
			return new String[]{e.getMessage()};
		}
	}
	private static int[] readLineInt(){
		try{
			String[] s = readLine();
			int[] ints = new int[s.length];
			for(int i=0;i<ints.length;i++) {
				ints[i] = Integer.parseInt(s[i]);
			}
			return ints;
		}catch(Exception e){
			e.printStackTrace();
			return null;
		}
	}
	private static long[] readLineLong(){
		try{
			String[] s = readLine();
			long[] ints = new long[s.length];
			for(int i=0;i<ints.length;i++) {
				ints[i] = Long.parseLong(s[i]);
			}
			return ints;
		}catch(Exception e){
			e.printStackTrace();
			return null;
		}
	}
	private static byte[] readLineByte(){
		try{
			String[] s = readLine();
			byte[] bytes = new byte[s.length];
			for(int i=0;i<bytes.length;i++) {
				bytes[i] = Byte.parseByte(s[i]);
			}
			return bytes;
		}catch(Exception e){
			e.printStackTrace();
			return null;
		}
	}
	private static char[] readLineChar(){
		try{
			String[] s = readLine();
			char[] chars = new char[s.length];
			for(int i=0;i<chars.length;i++) {
				chars[i] = (char)Integer.parseInt(s[i]);
			}
			return chars;
		}catch(Exception e){
			e.printStackTrace();
			return null;
		}
	}
	private static void print(Object o){
		System.out.println(o);
	}
	private static void print(){
		System.out.println();
	}
	private static void printd(Object o){
		if(MODE_DEBUG)System.err.println(o);
	}
	private static void printd(){
		if(MODE_DEBUG)System.err.println();
	}
}