Problem:
Score : 100 points

Problem Statement

How many ways are there to choose two distinct positive integers totaling N, disregarding the order?

Constraints

1 \leq N \leq 10^6

N is an integer.

Input

Input is given from Standard Input in the following format:

N

Output

Print the answer.

Sample Input 1

4

Sample Output 1

1

There is only one way to choose two distinct integers totaling 4: to choose 1 and 3. (Choosing 3 and 1 is not considered different from this.)

Sample Input 2

999999

Sample Output 2

499999

Solution in C (GCC 5.4.1) (judge verdict: Accepted)

#include <stdio.h>
#include <stdint.h>
           
           
int        
main (void)
{          
  uint32_t  N, i, count = 0;
           
  scanf("%d", &N);
           
  for (i = 1; i < (N + 1)/2; i++) {
    if (i != N -i) {
      count++;
    }      
  }        
           
  printf("%u", count);
           
  return 0;                                                                        
}