View Compilation Error

0_0_29967862_28583.cpp: In function '__int128 ksm(ll, ll)':
0_0_29967862_28583.cpp:11:28: error: 'mod' was not declared in this scope
         if (b&1) res=res*a%mod;
                            ^
0_0_29967862_28583.cpp:12:15: error: 'mod' was not declared in this scope
         a=a*a%mod;
               ^
0_0_29967862_28583.cpp:16:1: error: expected ';' before '}' token
 }
 ^