#include <stdio.h>
int my_length(char c[]) {
int len = 0;
int i = 0;
while (c[i] != '\0') {
len++;
i++;
}
return len;
}
int is_same(char *s1, char *s2) {
int i = 0;
int len1 = my_length(s1);
int len2 = my_length(s2);
while (*s1 != '\0' && *s2 != '\0') {
if (s1[i] != s2[i]) {
return i;
}
i++;
}
if (len1 == len2) {
return -1;
}
if (len1 < len2) {
return len1;
}
if (len1 > len2) {
return len2;
}
}
int main() {
char a1[1001], a2[1001];
int i1 = 0, i2 = 0;
char b;
while (i1 < 1000 && (b = getchar()) != '\n') {
a1[i1] = b;
i1++;
}
a1[i1] = '\0';
while (i2 < 1000 && (b = getchar()) != '\n') {
a2[i2] = b;
i2++;
}
a2[i2] = '\0';
printf("%d", is_same(a1, a2));
return 0;
}