ソースコード
#include <bits/stdc++.h>
#define fi first
#define se second
#define rep(i,n) for(int i = 0; i < (n); ++i)
#define rrep(i,n) for(int i = 1; i <= (n); ++i)
#define drep(i,n) for(int i = (n)-1; i >= 0; --i)
#define srep(i,s,t) for (int i = s; i < t; ++i)
#define rng(a) a.begin(),a.end()
#define maxs(x,y) (x = max(x,y))
#define mins(x,y) (x = min(x,y))
#define limit(x,l,r) max(l,min(x,r))
#define lims(x,l,r) (x = max(l,min(x,r)))
#define isin(x,l,r) ((l) <= (x) && (x) < (r))
#define pb push_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcountll
#define uni(x) x.erase(unique(rng(x)),x.end())
#define snuke srand((unsigned)clock()+(unsigned)time(NULL));
#define show(x) cout<<#x<<" = "<<x<<endl;
#define PQ(T) priority_queue<T,v(T),greater<T> >
#define bn(x) ((1<<x)-1)
#define dup(x,y) (((x)+(y)-1)/(y))
#define newline puts("")
#define v(T) vector<T>
#define vv(T) v(v(T))
using namespace std;
typedef long long int ll;
typedef unsigned uint;
typedef unsigned long long ull;
typedef pair<int,int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
inline int in() { int x; scanf("%d",&x); return x;}
template<typename T>inline istream& operator>>(istream&i,v(T)&v)
{rep(j,sz(v))i>>v[j];return i;}
template<typename T>string join(const v(T)&v)
{stringstream s;rep(i,sz(v))s<<' '<<v[i];return s.str().substr(1);}
template<typename T>inline ostream& operator<<(ostream&o,const v(T)&v)
{if(sz(v))o<<join(v);return o;}
template<typename T1,typename T2>inline istream& operator>>(istream&i,pair<T1,T2>&v)
{return i>>v.fi>>v.se;}
template<typename T1,typename T2>inline ostream& operator<<(ostream&o,const pair<T1,T2>&v)
{return o<<v.fi<<","<<v.se;}
template<typename T>inline ll suma(const v(T)& a) { ll res(0); for (auto&& x : a) res += x; return res;}
const double eps = 1e-10;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;
#define dame { puts("-1"); return 0;}
#define yn {puts("YES");}else{puts("NO");}
const int MX = 200005;
// coordinate compression
struct X {
typedef int T;
vector<T> d;
X() {}
X(vector<T>& a): d(a) {
init();
for (T& na : a) na = (*this)(na);
}
void add(T x) { d.pb(x);}
void init() {
sort(rng(d));
d.erase(unique(rng(d)), d.end());
}
int size() const { return sz(d);}
T operator[](int i) const { return d[i];}
int operator()(T x) const { return upper_bound(rng(d),x)-d.begin()-1;}
};
//
// Mod int
const int mod = 1000000007;
struct mint {
ll x;
mint():x(0){}
mint(ll x):x((x%mod+mod)%mod){}
// mint(ll x):x(x){}
mint& fix() { x = (x%mod+mod)%mod; return *this;}
mint operator-() const { return mint(0) - *this;}
mint& operator+=(const mint& a){ if((x+=a.x)>=mod) x-=mod; return *this;}
mint& operator-=(const mint& a){ if((x+=mod-a.x)>=mod) x-=mod; return *this;}
mint& operator*=(const mint& a){ (x*=a.x)%=mod; return *this;}
mint operator+(const mint& a)const{ return mint(*this) += a;}
mint operator-(const mint& a)const{ return mint(*this) -= a;}
mint operator*(const mint& a)const{ return mint(*this) *= a;}
bool operator<(const mint& a)const{ return x < a.x;}
bool operator==(const mint& a)const{ return x == a.x;}
};
istream& operator>>(istream&i,mint&a){i>>a.x;return i;}
ostream& operator<<(ostream&o,const mint&a){o<<a.x;return o;}
typedef vector<mint> vm;
//
int main() {
int n;
scanf("%d",&n);
vi a(n);
cin>>a;
X xs(a);
n = sz(xs);
vi s(n);
rep(i,sz(a)) s[a[i]]++;
mint dp = s[0];
rrep(i,n-1) {
dp += dp*s[i];
}
cout<<dp<<endl;
return 0;
}