import java.util.Scanner;
public class Main {
public static void main(String[] args) {
// TODO Auto-generated method stub
Scanner sc =new Scanner(System.in);
String s = sc.next();
//判断a长度不为1
while (s.length()>1) {
//则每位相加
int sum =0;
for (int i = 0; i < s.length(); i++) {
sum+=s.charAt(i)-48;
}
s=sum+"";
}
System.out.println(s);
}
}