View Compilation Error

0_0_18193603_25494.cpp: In function 'int main()':
0_0_18193603_25494.cpp:2:67: error: '__gcd' is not a member of 'std'
 int main(){int a,b;while(scanf("%d%d",&a,&b)==2)printf("%d\n",a*b/std::__gcd(a,b));}
                                                                   ^