关于enum的函数 问什么调不通

#include <iostream>

using namespace std;

int main()
{
enum week { Mon = 5, Tue, Wed, Thu = 55, Fri, Sta, Sun };

week day = 6;
cout << "day" << day << endl;
}

wangkai@ubuntu:~/Test$ g++ wangkai.cpp
wangkai.cpp: In function ‘int main()’:
wangkai.cpp:9: error: invalid conversion from ‘int’ to ‘main()::week’
wangkai@ubuntu:~/Test$