/* 
 *         　　exp 定積分 その0
 */
#include <math.h>
#include <stdio.h>

void main(void)
{
  int    j;
  int    ntrial;
  double x0 = 0.0, y0;
  double s = 0.0;
  double h;

  printf("Input: Number of trials:\n");
  scanf("%u", &ntrial);
  h=1.0/ntrial;

  j = 0;
  x0 = x0;
  y0 = exp(-x0);
  s = s + 0.5*y0;

  for (j = 1; j <= ntrial-1; j ++) {
    x0 = x0 + h;
    y0 = exp(-x0);
    s = s + y0;
  }

  j = j +1;
  x0 = x0 + h;
  y0 = exp(-x0);
  s = s + 0.5*y0;

  s = s / ntrial;
  printf("s = %1.6f \n", s);
}