Scanf читает данные дважды

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
 
int main() 
{
  double p1_x, p1_y; //Coordinate of first point  
  double p2_x, p2_y; //Coordinate of second point  
  double p3_x, p3_y; //Coordinate of third point  
int scanf_rtn; // Value returned by scanf() about number of successfully read values   char ch;
  
  printf("Enter first point (p1): ");
  scanf_rtn = scanf(" ( %lf , %lf %c ", &p1_x, &p1_y, &ch);
  if ( ( scanf_rtn != 3 ) || ( ch != ')' ) )
  {
    printf("Illegal input format!\n"); 
    system("pause");
    return -1;
  }    
  printf("Enter second point (p2): ");
  if ( (scanf(" ( %lf , %lf %c ", &p2_x, &p2_y, &ch) != 3 ) || ( ch != ')' ) )
  {
    printf("Illegal input format!\n"); 
    system("pause");
    return -1;
  }    
  printf("Enter third point (p3): ");
  if ( (scanf(" ( %lf , %lf %c ", &p3_x, &p3_y, &ch) != 3 ) || ( ch != ')' ) ) 
  {
    printf("Illegal input format!\n"); 
    system("pause");
    return -1;
  }    
  if (fabs((p3_y - p1_y)*(p2_x - p1_x) - (p2_x - p1_y)*(p3_x - p1_x)) < 0.001 )
  {
    printf("Illegal input, the three points are on one line.\n");
    system("pause");
    return -1;
  }               
  system("pause");
  return 0;
}