// ---------- begin ModInt ----------
const MOD: u32 = 1_000_000_007;

#[derive(Clone, Copy)]
struct ModInt(u32);

impl std::ops::Add for ModInt {
    type Output = ModInt;
    fn add(self, rhs: ModInt) -> Self::Output {
        let mut d = self.0 + rhs.0;
        if d >= MOD {
            d -= MOD;
        }
        ModInt(d)
    }
}

impl std::ops::AddAssign for ModInt {
    fn add_assign(&mut self, rhs: ModInt) {
        *self = *self + rhs;
    }
}

impl std::ops::Sub for ModInt {
    type Output = ModInt;
    fn sub(self, rhs: ModInt) -> Self::Output {
        let mut d = self.0 + MOD - rhs.0;
        if d >= MOD {
            d -= MOD;
        }
        ModInt(d)
    }
}

impl std::ops::SubAssign for ModInt {
    fn sub_assign(&mut self, rhs: ModInt) {
        *self = *self - rhs;
    }
}

impl std::ops::Mul for ModInt {
    type Output = ModInt;
    fn mul(self, rhs: ModInt) -> Self::Output {
        ModInt((self.0 as u64 * rhs.0 as u64 % MOD as u64) as u32)
    }
}

impl std::ops::MulAssign for ModInt {
    fn mul_assign(&mut self, rhs: ModInt) {
        *self = *self * rhs;
    }
}

impl std::ops::Neg for ModInt {
    type Output = ModInt;
    fn neg(self) -> Self::Output {
        ModInt(if self.0 == 0 {0} else {MOD - self.0})
    }
}

impl std::fmt::Display for ModInt {
    fn fmt<'a>(&self, f: &mut std::fmt::Formatter<'a>) -> std::fmt::Result {
        write!(f, "{}", self.0)
    }
}

impl std::str::FromStr for ModInt {
    type Err = std::num::ParseIntError;
    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let val = s.parse::<u32>()?;
        Ok(ModInt::new(val))
    }
}

#[allow(dead_code)]
impl ModInt {
    pub fn new(n: u32) -> ModInt {
        ModInt(n % MOD)
    }
    pub fn zero() -> ModInt {
        ModInt(0)
    }
    pub fn one() -> ModInt {
        ModInt(1)
    }
    pub fn pow(self, mut n: u32) -> ModInt {
        let mut t = ModInt::one();
        let mut s = self;
        while n > 0 {
            if n & 1 == 1 {
                t *= s;
            }
            s *= s;
            n >>= 1;
        }
        t
    }
    pub fn inv(self) -> ModInt {
        assert!(self.0 > 0);
        self.pow(MOD - 2)
    }
}
// ---------- end ModInt ----------
// ---------- begin Precalc ----------
#[allow(dead_code)]
struct Precalc {
    inv: Vec<ModInt>,
    fact: Vec<ModInt>,
    ifact: Vec<ModInt>,
}

#[allow(dead_code)]
impl Precalc {
    pub fn new(n: usize) -> Precalc {
        let mut inv = vec![ModInt::one(); n + 1];
        let mut fact = vec![ModInt::one(); n + 1];
        let mut ifact = vec![ModInt::one(); n + 1];
        for i in 2..(n + 1) {
            inv[i] = -inv[MOD as usize % i] * ModInt(MOD / i as u32);
            fact[i] = fact[i - 1] * ModInt(i as u32);
            ifact[i] = ifact[i - 1] * inv[i];
        }
        Precalc {
            inv: inv,
            fact: fact,
            ifact: ifact,
        }
    }
    pub fn inv(&self, n: usize) -> ModInt {
        self.inv[n]
    }
    pub fn fact(&self, n: usize) -> ModInt {
        self.fact[n]
    }
    pub fn ifact(&self, n: usize) -> ModInt {
        self.ifact[n]
    }
    pub fn comb(&self, n: usize, k: usize) -> ModInt {
        if k > n {
            return ModInt::zero();
        }
        self.fact[n] * self.ifact[k] * self.ifact[n - k]
    }
}
// ---------- end Precalc ----------

use std::io::Read;

// BB, RR があったら次の状態が一意に定まるはず
// BRBRB.. みたいな交互だったら次の状態は2通り、どちらも交互
// 上から塗ってマージしていくことができそう?

// 連続、交互
fn calc(h: &mut [u32]) -> (ModInt, ModInt) {
    let mut g = vec![];
    g.extend_from_slice(h);
    let d = h.iter().cloned().min().unwrap();
    for h in h.iter_mut() {
        *h -= d;
    }
    if *h.iter().max().unwrap() == 0 {
        let (x, y) = (ModInt(2).pow(h.len() as u32) - ModInt(2), ModInt(2).pow(d));
        return (x, y);
    }
    let mut a = vec![];
    let mut cnt = 0;
    let mut l = 0;
    while l < h.len() {
        if h[l] == 0 {
            cnt += 1;
            l += 1;
        } else {
            let mut r = l + 1;
            while r < h.len() && h[r] > 0 {
                r += 1;
            }
            a.push(calc(&mut h[l..r]));
            l = r;
        }
    }
    let mut x = ModInt::one();
    let mut y = ModInt(2);
    for a in a.iter() {
        x *= a.0 + a.1 * ModInt(2);
        y *= a.1;
    }
    let (x, y) = (x * ModInt(2).pow(cnt) - y, y);
    let y = y * ModInt(2).pow(d - 1);
    (x, y)
}

fn run() {
    let mut s = String::new();
    std::io::stdin().read_to_string(&mut s).unwrap();
    let mut it = s.trim().split_whitespace();
    let n: usize = it.next().unwrap().parse().unwrap();
    let mut h: Vec<u32> = it.map(|s| s.parse().unwrap()).collect();
    if n == 1 {
        let ans = ModInt(2).pow(h[0]);
        println!("{}", ans);
        return;
    }
    let mut ans = ModInt::one();
    if h[0] > h[1] {
        ans *= ModInt(2).pow(h[0]- h[1]);
        h[0] = h[1];
    }
    if h[n - 1] > h[n - 2] {
        ans *= ModInt(2).pow(h[n - 1]- h[n - 2]);
        h[n - 1] = h[n - 2];
    }
    for i in 1..(n - 1) {
        let d = std::cmp::max(h[i - 1], h[i + 1]);
        if h[i] > d {
            ans *= ModInt(2).pow(h[i] - d);
            h[i] = d;
        }
    }
    let (a, b) = calc(&mut h);
    ans *= a + b;
    println!("{}", ans);
}

fn main() {
    run();
}


Measured memory_bytes: 4352