#include <stdio.h>
#include <math.h>

int main() {

  double sum = 1;
  
  double p_factorial = 1;
  int max_itr = 20;

  for (int p = 1; p <= max_itr; p++) {
    p_factorial *= p;
    sum += 1/p_factorial;
  }

  printf("sum= %.20f\n", sum);
  printf(" e = %.20f\n", M_E);
  printf("|sum-e|=%e\n", fabs(sum-M_E));
  
  return 0;
}