/**
 * code generated by JHelper
 * More info: https://github.com/AlexeyDmitriev/JHelper
 * @author tatsumack
 */

#include <iostream>
#include <fstream>

#include <iostream>
#include <limits.h>
#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>

#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
#include <queue>
#include <unordered_map>
#include <unordered_set>

#define int long long
#define REP(i, n) for (int i = 0, i##_len = (n); i < i##_len; ++i)
#define REPS(i, n) for (int i = 1, i##_len = (n); i <= i##_len; ++i)
#define FOR(i, a, b) for (int i = (a), i##_len = (b); i <= i##_len; ++i)
#define REV(i, a, b) for (int i = (a); i >= (b); --i)
#define CLR(a, b) memset((a), (b), sizeof(a))
#define DUMP(x) cout << #x << " = " << (x) << endl;
#define INF 1001001001001001001ll
#define fcout cout << fixed << setprecision(12)

using namespace std;

typedef pair<int, int> P;

int mod = 1e9 + 7;

struct mint {
    unsigned x;

    mint() : x(0) {}

    mint(signed sig) { x = sig < 0 ? sig % mod + mod : sig % mod; }

    mint(signed long long sig) { x = sig < 0 ? sig % mod + mod : sig % mod; }

    int get() const { return (int) x; }

    mint& operator+=(mint that) {
        if ((x += that.x) >= mod) x -= mod;
        return *this;
    }

    mint& operator-=(mint that) {
        if ((x += mod - that.x) >= mod) x -= mod;
        return *this;
    }

    mint& operator*=(mint that) {
        x = (unsigned long long) x * that.x % mod;
        return *this;
    }

    mint& operator/=(mint that) { return *this *= that.inverse(); }

    mint operator+(mint that) const { return mint(*this) += that; }

    mint operator-(mint that) const { return mint(*this) -= that; }

    mint operator*(mint that) const { return mint(*this) *= that; }

    mint operator/(mint that) const { return mint(*this) /= that; }

    mint inverse() const {
        long long a = x, b = mod, u = 1, v = 0;
        while (b) {
            long long t = a / b;
            a -= t * b;
            std::swap(a, b);
            u -= t * v;
            std::swap(u, v);
        }
        return mint(u);
    }

    bool operator==(mint that) const { return x == that.x; }

    bool operator!=(mint that) const { return x != that.x; }

    mint operator-() const {
        mint t;
        t.x = x == 0 ? 0 : mod - x;
        return t;
    }
};

class ARobotRacing {
public:
    static constexpr int kStressIterations = 0;

    static void generateTest(std::ostream& test) {
    }

    void solve(std::istream& cin, std::ostream& cout) {
        int n;
        cin >> n;

        vector<int> x(n);
        REP(i, n) cin >> x[i];

        vector<mint> fact(100005);
        fact[0] = fact[1] = 1;
        FOR(i, 2, 100000) fact[i] = fact[i - 1] * i;

        mint res = 1;
        stack<int> stack;
        REP(i, n) {
            int pos = x[i];
            stack.push(pos);
            int n = (int) stack.size();
            if (pos < 2 * n - 1) {
                res *= n;
                stack.pop();
            }
        }
        res *= fact[stack.size()];
        cout << res.get() << endl;
    }
};;


signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
    std::istream& in(std::cin);
    std::ostream& out(std::cout);

    ARobotRacing solver;
    solver.solve(in, out);
    return 0;
}


Measured memory_bytes: 2304