#include<bits/stdc++.h>
#define ll long long
#define N 1005
using namespace std;
int read(){
    int x=0,f=1;char ch=getchar();
    while(ch<'0' && ch>'9')f=(ch=='-'?-1:f),ch=getchar();
    while(ch>='0' && ch<='9')x=(x<<1)+(x<<3)+(ch^48),ch=getchar();
    return x*f;
}
void write(int x){
    if(x<0)x=-x,putchar('-');
    if(x/10)write(x/10);
    putchar(x%10+'0');
}
int n,m,p;
double f[N][N];
double chkmin(double x,double y){
    if(x-y<1e-9)return x;
    else return y;
}
double dfs(int x,int y){
    if(f[x][y])return f[x][y];
    if(x==1 && y==1)return 0;
    if(x==1){
        return f[x][y]=dfs(x,y-1)+p*1.0/4;
    }
    else if(y==1){
        return f[x][y]=dfs(x-1,y)+p*1.0/4;
    }
    else{
        double A=dfs(x,y-1),B=dfs(x-1,y),res=0;
        if(B<A)swap(A,B);
        if(A+p<B)return A+p*1.0/4;
        return f[x][y]=(A+p-B)*B*1.0/p/2+A/2+(B-A)*(A+B)/p/4;
    }
}
int main(){
    #ifdef EAST_CLOUD
    freopen("a.in","r",stdin);
    freopen("a.out","w",stdout);
    #endif
    n=read(),m=read(),p=read();
    printf("%.10lf",dfs(n,m));
    return 0;
}