I'm very new to programming and I'm trying to make a program to compute the circumference of a circle when you give it the radius, but I keep getting "fatal error LNK1169: one or more multiply defined symbols found" whenever I think I fix it, it just says the same thing. What am I doing wrong?

```
#include <iostream>
#include <cstdlib>
#include <cmath>
using namespace std;
//////////////////////////////////////////////////////////
double pi = 3.14159265359;
int main()
{
float r;
float circumference;
float pi;
cout << "What is the radius of the circle: ";
cin >> r;
circumference = 2 * pi * r;
cout << "The circumference is " << circumference << '.' << endl;
system("PAUSE");
return(0);
} // end main
```