size of struct in C

Possible Duplicate:
Why isn’t sizeof for a struct equal to the sum of sizeof of each member?

Consider the following C code:

#include <stdio.h>    

struct employee
{
  int id;
  char name[30];  
};

int main()
{
  struct employee e1;      
  printf("%d %d %d", sizeof(e1.id), sizeof(e1.name), sizeof(e1));
  return(0);
}

The output is:

4 30 36

Why is the size of the structure not equal to the sum of the sizes of its individual component variables?