#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
using namespace std;
#define eps 1e-8
int main()
{
double h, H, l;
scanf("%lf %lf %lf", &h, &H, &l);
H /= 2;
double left, right, tmp, mid1, mid2, ans1, ans2;
left = eps;
tmp = sqrt(H*H - h*h);
if (tmp <= l)
right = tmp;
else
right = l;
while (fabs(right - left) > eps) {
mid1 = (left + right) / 2;
mid2 = (left + mid1) / 2;
ans1 = mid1*H/sqrt(mid1*mid1+h*h) - mid1;
ans2 = mid2*H/sqrt(mid2*mid2+h*h) - mid2;
if (ans1 > ans2)
left = mid2;
else
right = mid1;
}
printf("%.6lf\n", ans1);
return 0;
}