package no176;

import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long a = sc.nextInt();
		long b = sc.nextInt();
		long t = sc.nextInt();
		long max = Math.min(a-1, (t+b-1)/b);
		long ans = Long.MAX_VALUE;
		for(int y=0;y<max;y++) {
			long x;
			if (b * y >= t) {
				x = 0;
			}else{
				x = (t - (long)b * y + a - 1) / a;
			}
			ans = Math.min(a * x + b * y, ans);
		}
		System.out.println(ans);
	}

}