#include
#include
using namespace std;
int main()
{
double l, l1, h, l2, pi = 3.14159265;
cout << "Input l1, h, l:";
cin >> l1;
cin >> h;
cin >> l;
l2 = l1 * (exp(2.0 * pi * h / l) - exp(-2.0 * pi * h /l)) / (exp(2.0 * pi * h /l) + exp(2.0 * pi * h / l));
while (fabs(l - l2) > 0.01)
{
l = l2;
l2 = l1 * (exp(2.0 * pi * h / l) - exp(-2.0 * pi * h /l)) / (exp(2.0 * pi * h /l) + exp(2.0 * pi * h / l));
}
cout << "L = " << l2 << "\n";
}