import java.util.*;
public class Main{
	public static void main(String[] args)throws Exception{
		new Main().solve();
	}
	void solve(){
		Scanner sc=new Scanner(System.in);
		int a=sc.nextInt();
		int b=sc.nextInt();
		int n=sc.nextInt();
		
		int min=999999999;
		for(int i=0;i<=b;i++){
			min=Math.min(a*i+((n-a*i+b-1)/b)*b, min);
		}
		
		System.out.println(min);
	}
}