//真是的AC代码都没有！！！

#include<bits/stdc++.h>
#define ll long long
using namespace std;
double p[1000005];
int n, L, R;
int main(){
	scanf("%d %d %d", &n, &L, &R); 
	double pk = 1.0 / (R - L + 1);
	p[0] = 1;
	double sump = 0;    //sump表示[i-R,i-L]区间概率之和
	for (int i = 1; i <= n; i++){
		if (i - L >= 0)sump += p[i - L];
		if (i - R - 1 >= 0)sump -= p[i - R - 1];
		p[i] = sump * pk;
	}
	printf("%.8f\n", p[n]);
	return 0;
}