text: #include <stdio.h>
  #include <math.h>
   
  int main() {
      double k, l;
      k = sin(108 * M_PI / 180) / sin(63 * M_PI / 180);
      while (scanf("%lf", &l) != EOF) {
          printf("%.10lf\n", l*k);
      }
      return 0;
  }
  