int a,b,c,d;
BigInteger ans;
// for x axis
if(x1>x2){
    a=x2;
    b=x1;
}else{
    a=x1;
    b=x2;
}
// for y axis
if(y1>y2){
    c=y2;
    d=y1;
}else{
    c=y1;
    d=y2;
}
// difference 
BigInteger x=new BigInteger(String.valueOf(b-a));
BigInteger y=new BigInteger(String.valueOf(d-c));
// gcd calculation
ans=x.gcd(y);
int i= ans.intValue();

return i-1;