//Man always remember love because of romance only!
#include<bits/stdc++.h>
using namespace std;
inline int read(){
    int n=0,w=0; char ch=0;
    while(!isdigit(ch)) {w|=ch=='-';ch=getchar();}
    while(isdigit(ch)) n=(n<<3)+(n<<1)+(ch^48),ch=getchar();
    return w?-n:n;
}
inline void write(int x){
	if(x<0) putchar('-'),x=-x;
    if(x>9) write(x/10);
    putchar(x%10+'0');
}
double dp[5001][5001];
int main(){
//	freopen(".in","r",stdin);
//	freopen(".out","w",stdout);
	int n=read(),m=read();
	double p;
	cin>>p;
	dp[n][m]=0;
	for(int i=n-1;i;i--) dp[i][m]=dp[i+1][m]+p/4;
	for(int i=m-1;i;i--) dp[n][i]=dp[n][i+1]+p/4;
	for(int i=n-1;i;i--){
		for(int j=m-1;j;j--){
			double x=dp[i+1][j],y=dp[i][j+1];
			if(x>y) swap(x,y);
			if(y-x<=p) dp[i][j]=x/2+(y-x)/2/p*(x+(y-x)/2)+(p-y+x)/p*y/2;
			else dp[i][j]=x+p/4;
		}
	} 
	cout<<setprecision(10)<<fixed<<dp[1][1];
	return 0;
}