View Compilation Error

0_0_23681145_3306.cpp:5:1: error: '_int64' does not name a type
 _int64 multi(_int64 a,_int64 b)
 ^
0_0_23681145_3306.cpp: In function 'int main()':
0_0_23681145_3306.cpp:28:29: error: 'multi' was not declared in this scope
         cout<<(multi(2,num-1)+1)%num<<endl;
                             ^