foo.cpp: In function 'int main()':
foo.cpp:4:1: error: 'cin' is not a member of 'std'
 std::cin>>n;
 ^
foo.cpp:5:20: error: 'sqrt' was not declared in this scope
 for (i=2;i<=sqrt (n);i++){
                    ^
foo.cpp:6:14: error: 'cout' is not a member of 'std'
 if (n%i==0){ std::cout<<n/i; return 0; } }
              ^