#include <iostream>
#include <cstdio>
using namespace std;
int S, a, n;
bool test(double p)
{
int T = S;
for (int i = 1; i <= n; i++)
{
T += p * T;
T -= a;
}
return T <= 0;
}
int main()
{
cin >> S >> a >> n;
double left = 0, right = 3;
while (right - left > 1e-4)
{
double mid = (left + right) / 2.0;
if (test(mid))
left = mid;
else
right = mid;
}
printf("%.1f", left * 100);
return 0;
}