题解 | #The Biggest Water Problem#

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        int a = sc.nextInt();
        int sumi;
        sumi = m5(a);
        while(sumi>=10){
            sumi = m5(sumi);
        }
        System.out.printf("%d",sumi);
    }
    public static int m5(int a){     //此函数的作用是取整数各位然后再将各位相加
        int sum = 0;
        int x;
        while(a!=0){
                x = a%10;
                a = a/10;
                sum = sum + x;
        }
        return sum;  //函数范围各个位数字之和
    }
}