View Compilation Error

0_0_26027662_27340.cpp: In function 'LL powmod(LL, LL)':
0_0_26027662_27340.cpp:29:52: error: 'assert' 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;}
                                                    ^