#include <stdio.h>
int suma(int a[]){
int sum=0,i=0;
while(a[i]!=EOF){
sum++;
i++;
}return sum;
}
int sumb(int b[]){
int sum=0,i=0;
while(b[i]!=EOF){
sum++;
i++;
}return sum;
}
int sum(int a[],int b[]){
int sizea=suma(a),sizeb=sumb(b);
if(sizea>sizeb){
return sizeb;
}if (sizea<sizeb){
return sizea;
}
if(sizea==sizeb){
int size=sizea;
for(int i=0;i<size;i++){
if(a[i]!=b[i]){
return i;
}
}
}
return -1;
}
int main() {
int a[1001],b[1001],answer=0;
char m,n;
int i=0,t=0;
while((m=getchar())!=EOF){
a[i]=m;
printf("%d",a[i]);
i++;
}
while((n=getchar())!=EOF){
b[t]=n;
t++;
}
answer=sum(a,b);
printf("%d",answer);
return 0;
}