

void main(){
	
	auto ABN = readLine!real();
	auto A = ABN[0];
	auto B = ABN[1];
	auto N = ABN[2];
	
	long maximum = long.min;
	long temp;
	
	foreach( i ; 0..N+1 ){

		maximum = cast(long)max( maximum , floor((A*i)/B) - A*floor(i/B) );
	}
	maximum.writeln();
	
}



import std.stdio, std.string, std.conv;
import std.math, std.algorithm, std.array, std.bigint;
import std.regex;

string alphabet = "abcdefghijklmnopqrstuvwxyz";

T[] readLine( T = size_t )( string sp = " " ){
	T[] ol;
	foreach( string elm ; readln().chomp().split(sp) ){
		ol ~= elm.to!T();
	}
	return ol;
}