Using "If Statements" in basic C programming. How can I properly format them?

To begin, the code that I have got up to this point is below.

The calculator does everything I want it to, minus the fact that it still includes negative numbers in its calculations. I would like for it to do nothing if the number presented as the radius is less than zero, yet still calculate if the number is non-negative. However, I am having issues with using an if statement. I have not used these before, as I am really just a beginner. I just need a push in the right direction. Do I need to have an "else"? Any help is greatly appreciated!

#include <stdio.h>

int radius, area;

main()
{
    printf("Enter radius: ");
    scanf("%d", &radius);
    {
    if (&radius > -1);  {
         area = (int)(3.14159 * radius * radius);
         printf("Area = %d\n", area);}
    else {
       return(0); }
    }
   return(0);
}