View Compilation Error

0_0_29923054_14433.cpp: In function 'void exgcd(long long int, long long int, long long int&, long long int&)':
0_0_29923054_14433.cpp:35:18: error: 'ex_gcd' was not declared in this scope
  ex_gcd(b,a%b,x,y);
                  ^
0_0_29923054_14433.cpp: In function 'long long int Inv(long long int, long long int)':
0_0_29923054_14433.cpp:43:16: error: 'ex_gcd' was not declared in this scope
  ex_gcd(a,b,x,y);
                ^