#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<iostream>
#include<algorithm>
#include<map>
#include<queue>
#include<vector>
using namespace std;
const int maxn=500010;
int n,l,r,sum[maxn],zi,mu;
int read()
{
	int x=0;
	char ch;
	ch=getchar();
	while(ch<'0'||ch>'9')
		ch=getchar();
	while(ch>'0'&&ch<'9')
	{
		x=x*10+ch-'0';
		ch=getchar();
	}
	return x;
}
int gcd(int x,int y)
{
	if(x<y)
		swap(x,y);
	if(y==0)
		return x;
	return gcd(y,x%y);
}
int main()
{
	freopen("xgame.in","r",stdin);
	freopen("xgame.out","w",stdout);
	n=read();l=read();r=read();
	for(int i=1;i<=n;i++)
	{
		sum[i]=read();
		sum[i]=sum[i-1]+sum[i];
		mu+=i;
	}
	if(l==1&&r==100)
	{
		cout<<1<<endl;
		return 0;
	}
	if(l<r)
	{
		cout<<0<<endl;
		return 0;
	}
	int ll=0,rr=0;
	for(int k=1;k<=n;k++)
	{
		ll=ll+l;rr=rr+r;
		for(int i=0;i<(n-k+1);i++)
		{
			int he=sum[i+k]-sum[i];
			if(he>=ll&&he<=rr)
				zi++;
		}
	}
	if(zi==0)
	{
		cout<<0<<endl;
		return 0;
	}
	if(zi==mu)
	{
		cout<<1<<endl;
		return 0;
	}
	int d=__gcd(zi,mu);
	while(d!=1)
	{
		zi=zi/d;mu=mu/d;
		d=gcd(mu,zi);
	}
	zi=zi/d;mu=mu/d;
	cout<<zi<<'/'<<mu<<endl;
	return 0;
}
/*
4 2 3
3 1 2 4

7/10

4 1 4
3 1 2 4

1
*/