View Compilation Error

0_0_37942269_29431.cpp: In function 'long long int rho(long long int)':
0_0_37942269_29431.cpp:26:38: error: 'gcd' was not declared in this scope
   for(ll x=0,y=0,i=0;i++%255||gcd(p,n)==1;x=f(x),y=f(f(y))){
                                      ^
0_0_37942269_29431.cpp:30:17: error: 'gcd' was not declared in this scope
   return gcd(p,n);
                 ^