#include <stdio.h>

int main () {
  char a[20], b[20];
  int lena=0, lenb=0, common=1;
  scanf("%s %s", a,b);

  /* determine the lengths of the strings--could have used strlen here */
  while ( a[lena]!='\0' ) {
    lena++;
  }
  while ( b[lenb]!='\0' ) {
    lenb++;
  }

  /* work backwards as long as the characters are the same */
  while ( a[lena-common] == b[lenb-common]
          && lena-common>=0 && lenb-common>=0 ) {
    common++;
  }

  printf("Common characters: %i\n", common-1);

}