#define _GNU_SOURCE
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

char* fcvt(double x, int n, int* dp, int* sign) {
  char tmp[1500];
  int i, lz;

  if (n > 1400U)
    n = 1400;
  sprintf(tmp, "%.*f", n, x);
  i = (tmp[0] == '-');
  if (tmp[i] == '0')
    lz = strspn(tmp + i + 2, "0");
  else
    lz = -(int)strcspn(tmp + i, ".");

  if (n <= lz) {
    *sign = i;
    *dp = 1;
    if (n > 14U)
      n = 14;
    return "000000000000000" + 14 - n;
  }

  return ecvt(x, n - lz, dp, sign);
}