#include <iostream>
#include <math.h>
#include <bits/stdc++.h>

using namespace std;
int BC(int n, int k)
{
    int C[k+1];
    memset(C, 0, sizeof(C));

    C[0] = 1;  // nC0 is 1

    for (int i = 1; i <= n; i++)
    {
        for (int j = min(i, k); j > 0; j--)
            C[j] = C[j] + C[j-1];
    }
    return C[k];
}

double sBern (int n, int k, double p) // n > k
{
    double q = 1 - p;
    double B_C = BC(n,k);
    return B_C * pow(p,k) * pow(q,n-k);
}

int main()
{
    ios_base::sync_with_stdio(0);
    double n,s,d;

    while(cin >> s >> d >> n)
    {
        //d = double(10)/3;
        s /= d;
        s /= d;
        double p=n/2, P=0;
        for(int i=n; i >= p; i--)
        {
            P += sBern(n,i,s);
        }
        cout << setprecision(16) << P << "\n";
    }
}


// 0.5 3.333333 10