View Compilation Error

0_0_30244195_4593.cpp: In function 'll pow(ll, ll)':
0_0_30244195_4593.cpp:21:30: error: 'mod' was not declared in this scope
         if (b&1) tr = (tr*a)%mod;
                              ^
0_0_30244195_4593.cpp:22:19: error: 'mod' was not declared in this scope
         a = (a*a)%mod;
                   ^
0_0_30244195_4593.cpp: In function 'int main()':
0_0_30244195_4593.cpp:37:30: error: 'mod' was not declared in this scope
             r[i] = pow(r[i], mod-2ll);
                              ^