#include<bits/stdc++.h>
using namespace std;
const int N=1010;
double dp[N][N];
int main()
{
    int r,c,p;
    scanf("%d %d %d",&r,&c,&p);
    dp[r][c]=0.00;
    for(int i=r;i>=1;i--)
    {
        for(int j=c;j>=1;j--)
        {
            if(i==r&&j==c)continue;
            else if(i==r)dp[i][j]=dp[i][j+1]+0.25*p;
            else if(j==c)dp[i][j]=dp[i+1][j]+0.25*p;
            else
            {
                double p1=dp[i][j+1];
                double p2=dp[i+1][j];
                if(p1-p2>=1.00*p)
                {
                    dp[i][j]=p2+0.25*p;
                }
                else if(p2-p1>=1.00*p)
                {
                    dp[i][j]=p1+0.25*p;
                }
                else
                {
                    if(p1*1.00>=p2*1.00)dp[i][j]=0.50*p2+0.50*(((p1*1.00-p2*1.00)/p)*(p2+0.50*(p1-p2))+((p-p1*1.00+p2*1.00)/p)*p1);
                    else dp[i][j]=0.50*p1+0.50*(((p2*1.00-p1*1.00)/p)*(p1+0.50*(p2-p1))+((p-p2*1.00+p1*1.00)/p)*p2);
                }
            }
        }
    }
    printf("%.8f\n",dp[1][1]);
    return 0;
}