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// #pragma GCC optimize("Ofast")
// #pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,tune=native")
// #pragma GCC optimize("unroll-loops")    
#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <numeric>
#include <cstring>
#include <ctime>
#include <cstdlib>
#include <set>
#include <map>
#include <unordered_map>
#include <unordered_set>
#include <list>
#include <cmath>
#include <bitset>
#include <cassert>
#include <queue>
#include <deque>
#include <cassert>
#include <iomanip> 
#include <chrono>
#define pb push_back
#define x first
#define y second
#define mp make_pair
#define files(FILENAME) read(FILENAME); write(FILENAME)
#define read(FILENAME) freopen((string(FILENAME) + ".in").c_str(), "r", stdin)
#define write(FILENAME) freopen((string(FILENAME) + ".out").c_str(), "w", stdout)
using namespace std;
        
template<typename T1, typename T2>inline void chkmin(T1 &x, T2 y) { if (x > y) x = y; }
template<typename T1, typename T2>inline void chkmax(T1 &x, T2 y) { if (x < y) x = y; } 
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const pair<T, U> &_p) { _out << _p.first << ' ' << _p.second; return _out; }
template<typename T, typename U> inline istream &operator>> (istream &_in, pair<T, U> &_p) { _in >> _p.first >> _p.second; return _in; }
template<typename T> inline ostream &operator<< (ostream &_out, const vector<T> &_v) { if (_v.empty()) { return _out; } _out << _v.front(); for (auto _it = ++_v.begin(); _it != _v.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline istream &operator>> (istream &_in, vector<T> &_v) { for (auto &_i : _v) { _in >> _i; } return _in; }
template<typename T> inline ostream &operator<< (ostream &_out, const set<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const multiset<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const unordered_set<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T> inline ostream &operator<< (ostream &_out, const unordered_multiset<T> &_s) { if (_s.empty()) { return _out; } _out << *_s.begin(); for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) { _out << ' ' << *_it; } return _out; }
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const map<T, U> &_m) { if (_m.empty()) { return _out; } _out << '(' << _m.begin()->first << ": " << _m.begin()->second << ')'; for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) { _out << ", (" << _it->first << ": " << _it->second << ')'; } return _out; }
template<typename T, typename U> inline ostream &operator<< (ostream &_out, const unordered_map<T, U> &_m) { if (_m.empty()) { return _out; } _out << '(' << _m.begin()->first << ": " << _m.begin()->second << ')'; for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) { _out << ", (" << _it->first << ": " << _it->second << ')'; } return _out; }
 
typedef long double base;        
typedef pair<int, int> point;

const int p = 1e9 + 7;

int a[101];

int sum(int a, int b) {
	a += b;
	return a < p ? a : a - p;
}

int mul(long long a, int b) {
	return a * b % p;
}

int powx(int a, int b) {
	int ans = 1;
	while (b) {
		if (b & 1) ans = mul(ans, a);
		a = mul(a, a);
		b >>= 1;
	}
	return ans;
}

const int rev2 = powx(2, p - 2);

int n;
int h[101];

pair<int, int> res(int Ln, int Rn, int cur_h) {
	int min_h = 1e9;
	for (int i = Ln; i < Rn; ++i) {
		chkmin(min_h, h[i]);
	}
	int L = Ln;
	int ans1 = 1, ans2 = 1, cnt0 = 0, cnt1 = 0;
	while (L < Rn) {
		if (h[L] == min_h) {
			++cnt0;
			++L;
			continue;
		}
		++cnt1;
		int R = L;
		while (R < Rn && h[R] != min_h) {
			++R;
		}
		auto rep = res(L, R, min_h);
		rep.x = sum(rep.x, rep.x);
		ans1 = mul(ans1, rep.x);
		ans2 = mul(ans2, mul(2, sum(rep.x, rep.y)));
		L = R; 
	}
	cnt0 = powx(2, cnt0);
	cnt1 = powx(2, cnt1);
	// cout << ans1 << ' ' << ans2 << ' ' << cnt0 << ' ' << cnt1 << endl;
	pair<int, int> ans = {0, 0};
	ans.x = mul(ans1, 2);
	ans.y = sum(mul(ans2, cnt0), p - ans.x);
	// cout << ans.x << ' ' << ans.y << endl;
	ans.x = mul(ans.x, powx(2, min_h - cur_h - 1));
	ans.x = mul(ans.x, rev2);
	ans.y = mul(ans.y, rev2);
	return ans;
}

int main() {
	ios::sync_with_stdio(0);
	srand(time(0));
	//read("input");
	cin >> n;
	for (int i = 0; i < n; ++i) {
		cin >> h[i];
	}
	auto rep = res(0, n, 0);
	cout << mul(2, sum(rep.x, rep.y)) << endl;
}

Measured memory_bytes: 256