#include<bits/stdc++.h>
#define ff first
#define ss second
#define pb push_back
typedef long long ll;
using namespace std;
typedef pair<int,int> pii;
typedef long double ld;

const int mod=998244353;
inline int add(int x,int y){int ret=x+y;if(ret>=mod)ret-=mod;return ret;}
inline int sub(int x,int y){int ret=x-y;if(ret<0)ret+=mod;return ret;}
inline int mul(int x,int y){return ((ll)x*y)%mod;}
inline int step(int base,int pw){int ret=1;while(pw){if(pw&1)ret=mul(ret,base);base=mul(base,base);pw>>=1;}return ret;}
inline int invv(int x){return step(x,mod-2);}


const int maxn=1000+10;

ld dp[maxn][maxn],nck[maxn][maxn];

ld get_nck(int n,int k){
    if(n<0 || k<0 || n<k)return 0;
    if(nck[n][k]!=-1)return nck[n][k];
    if(k==0)return 1;
    nck[n][k]=get_nck(n-1,k)+get_nck(n-1,k-1);
    return nck[n][k];
}

int n,d,r;

ld go(int n,int d){

    ///printf("%d %d SS\n",n,d);

    if(d<0)return 0;
    if(n==0)return 0;
    ld pom=get_nck(d+n-1,n-1);
    if(n<=r)return (n+d)*pom;
    if(dp[n][d]!=-1)return dp[n][d];

    ///printf("%d %d RACUNA\n",n,d);

    ld &a=dp[n][d];
    a=0;

    for(int g=0;g<=n;g++){
        a+=get_nck(n,g)*go(n-g,d-n+g);
    }

    a+=pom*r;

    ///cout<<n<<" "<<d<<" "<<a<<endl;
    return a;
}

int main(){

    ///freopen("test.txt","r",stdin);

    for(int i=0;i<maxn;i++)
    for(int j=0;j<maxn;j++){
        dp[i][j]=-1;
        nck[i][j]=-1;
    }

    scanf("%d %d %d",&n,&d,&r);

    cout<<fixed<<setprecision(10)<<go(n,d)/get_nck(d+n-1,n-1);


    return 0;
}