#include <stdio.h>

#include <math.h>

​

int main() {

  const double E = 2.718281828;

​

  printf("%f\n", log(6.0));

  printf("%f\n", log(E));

  printf("%f\n", log(2.0));

  printf("%f\n", log(1.0));

  printf("%f\n", log(0.0));

  printf("%f\n", log(-1.0));

  return 0;

}