#include <stdio.h>

int main(int argc, char *argv[])
{
  int i, chksum=0;

  for (i=0; i<12; i+=2) {
    cksum += argv[0][i]-'0' + 3*(argv[0][i+1]-'0');
  }
  printf("%d\n", 9-(cksum-1)%10);
}