View Compilation Error

0_0_25931208_11140.cpp: In function 'LL powmod(LL, LL)':
0_0_25931208_11140.cpp:15:35: error: 'mod' was not declared in this scope
 LL powmod(LL a,LL b) {LL res=1;a%=mod; assert(b>=0); for(;b;b>>=1){if(b&1)res=res*a%mod;a=a*a%mod;}return res;}
                                   ^