/*One Night Of The Hunters*/
#include<cstdio>
#include<cstdlib>
#include<iostream>
#include<cstring>
#include<algorithm>
#include<queue>
#include<iomanip>
#include<stack>
#include<map>
#include<set>
#include<cmath>
#define debug(x) cerr<<#x<<"="<<x<<endl
#define INF 0x7f7f7f7f
using namespace std;
typedef pair<int,int> pii;
typedef long long ll;
inline int init()
{
	int now=0,ju=1;char c;bool flag=false;
	while(1)
	{
		c=getchar();
		if(c=='-')ju=-1;
		else if(c>='0'&&c<='9')
		{
			now=now*10+c-'0';
			flag=true;
		}
		else if(flag)return now*ju;
	}
}
inline long long llinit()
{
	long long now=0,ju=1;char c;bool flag=false;
	while(1)
	{
		c=getchar();
		if(c=='-')ju=-1;
		else if(c>='0'&&c<='9')
		{
			now=now*10+c-'0';
			flag=true;
		}
		else if(flag)return now*ju;
	}
}
ll ans=0;
#ifdef unix
#define LL "%lld"
#else
#define LL "%I64d"
#endif

int n,l,r,a[500001];
int temp[500001];

long long gcd(long long a,long long b)
{
	if (!b) return a;
	else return gcd(b,a%b);
}

int main()
{
	freopen("xgame.in","r",stdin);
	freopen("xgame.out","w",stdout);
	n=init();l=init();r=init();
	for(int i=1;i<=n;i++)
	{
		a[i]=init();
	}
	Mergesort(1,n);
	ll down=(n*(n+1))/2;
	ll g=gcd(ans,down);
	ans/=g;down/=g;
	if(ans==g)
	{
		printf("1\n");
	}
	else
	{
		if(ans==0)
		{
			printf("0");
		}
		else printf(LL"/"LL"\n",ans,down);
	}
	return 0;
}