View Compilation Error

0_0_25361995_23694.cpp: In function 'long long int ola(long long int)':
0_0_25361995_23694.cpp:8:6: error: 'i' was not declared in this scope
  for(i=2;i*i<=n;i++)
      ^
0_0_25361995_23694.cpp: In function 'int main()':
0_0_25361995_23694.cpp:29:25: error: 'mod' was not declared in this scope
   ans=(ans-(n*ola(n)/2)%mod+mod)%mod;
                         ^