int output(int n) {
while (1) {
n = n % 10 + n / 10;
if (n >= 10) output(n);
else return n;
}
}
int main() {
int n, sum;
scanf("%d", &n);
printf("%d", output(n));
return 0;
}
int output(int n) { while (1) { n = n % 10 + n / 10; if (n >= 10) output(n)" >
int output(int n) {
while (1) {
n = n % 10 + n / 10;
if (n >= 10) output(n);
else return n;
}
}
int main() {
int n, sum;
scanf("%d", &n);
printf("%d", output(n));
return 0;
}