题解 | 清楚姐姐买竹鼠

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        
        int a = in.nextInt();
        int b = in.nextInt();
        int n = in.nextInt();

        if (b / 3 >= a) System.out.println((long) a * n);
        else {
            System.out.println((long) n / 3 * b + Math.min((n % 3) * a, b));
        }
        
    }
}