#include"stdio.h"
void main()
{
	char m;
	int sum;
	scanf("%c",&m);
	while(m!='0')
	{
		sum=0;
		while(m!=10)
		{
			sum+=m-48;
			scanf("%c",&m);
		}
		sum=sum%9;
		if(sum==0)
			sum=9;
		printf("%d\n",sum);
		scanf("%c",&m);
	}
}