#include <stdlib.h>
#include <stdio.h>
#include <stdbool.h>
double min(double a, double b)
{
    if(a<b)
        return a;
    return b;
}
int main()
{
    long a, h, w;
    scanf("%d",&a);
    scanf("%d",&h);
    scanf("%d",&w);
    double x = 10000000000;
    bool t = false;
    for (int k = 1; k * a <= h; k++)
    {
        long l = ( a * k + k * w + w - h) / (a + h);
        if (l>=0 && (h - a * k) * (l + 1) == (w - a * l) * (k + 1))
        {
            t = true;
            x = min(x, ((double)(h - a * k)) / ((double)(k + 1)));
        }
    }
    if (t)
        printf("%f",x);
    else
        printf("-1");
    return 0;
}