#include <stdio.h>

#include <math.h>

int main() {

   const double e = 0.1 * pow(10, -5), b = 0.5 * pow(10, -6);

   double N = 123, a = 34.5 * pow(10, -8);

   double l = (sqrt(pow(e, 2) + fabs(log(b / a)))) / (2 * N * e);

   printf("result: %lf", l);

   return 0;

}