#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define R cin>>
#define ll long long
#define ln cout<<'\n'
#define in(a) insert(a)
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n",a)
#define mem(a) memset(a,0,sizeof(a))
#define all(c) (c).begin(),(c).end()
#define iter(c) __typeof((c).begin())
#define rrep(i,n) for(ll i=(ll)(n)-1;i>=0;i--)
#define REP(i,m,n) for(ll i=(ll)(m);i<(ll)(n);i++)
#define rep(i,n) REP(i,0,n)
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
ll check(ll n,ll m,ll x,ll y){return x>=0&&x<n&&y>=0&&y<m;}void pr(){ln;}
template<class A,class...B>void pr(const A &a,const B&...b){cout<<a<<(sizeof...(b)?" ":"");pr(b...);}
template<class A>void PR(A a,ll n){rep(i,n)cout<<(i?" ":"")<<a[i];ln;}
const ll MAX=1e9+7,MAXL=1LL<<61,dx[8]={-1,0,1,0,-1,-1,1,1},dy[8]={0,1,0,-1,-1,1,1,-1};
typedef pair<ll,ll> P;

void Main() {
  ll n;
  R n;
  vector<ll> a(n+1,0);
  rep(i,n) R a[i];
  sort(all(a));
  a.erase(unique(all(a)),a.end());
  ll ans=1;
  rrep(i,a.size()-1) {
    ans*=a[i+1]-a[i]+1;
    ans%=MAX;
  }
  pr(ans);
}

int main(){ios::sync_with_stdio(0);cin.tie(0);Main();return 0;}

#include <bits/stdc++.h>

#define pb push_back
#define mp make_pair
#define ff first
#define ss second
#define all(x) (x).begin(), (x).end()
#define ll long long
#define ii pair<int,int>
#define vi vector<int>
#define vll vector<ll>
#define vii vector<ii>
#define ar array

const int INF = 0x3f3f3f3f;
const ll  LINF = 0x3f3f3f3f3f3f3f3fLL;
const int maxn = 2e5+10;
const int mod = 1e9+7;

using namespace std;

void solve(){
	double s1,s2,g1,g2;
	cin >> s1 >> s2 >> g1 >> g2;
	double ans = (g2*s1+s2*g1)/(s2+g2);
	cout << setprecision(10) << ans << endl;
}

int32_t main(){
    ios_base::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);

    int t = 1;

    // cin >> t;

    while(t--){
    	solve();
    }

    return 0;
}

