#include <stdio.h>
#include <string.h>

int SigDigit(int nInput)
{
	if (nInput < 10)
		return nInput;
	int nSum = 0;
	while(nInput != 0)
	{
		nSum += nInput % 10;
		nInput /= 10;
	}
	return SigDigit(nSum);
}

int main(int argc, char* argv[])
{
	char pInput[2000];
	unsigned int nInput = 0;
	while(scanf("%s", pInput), pInput[0] != '0')
	{
		nInput = 0;
		for (int i = 0; i < strlen(pInput); i++)
		{
			nInput += pInput[i] - '0';
		}
		printf("%d\n", SigDigit(nInput));
	}
	return 0;
}