#include <stdio.h>
int main()
{
double f,c;
scanf("%lf",&f);
c=5/(9/(f-32));
printf("%.3lf\n",c);
return 0;
}

#include <stdio.h>
int main()
{
double f,c;
scanf("%lf",&f);
c=5/(9/(f-32));
printf("%.3lf\n",c);
return 0;
}