#![allow(unused_imports, unused_variables, dead_code, non_snake_case, unused_macros)]
use std::io::{stdin, Read, StdinLock};
use std::str::FromStr;
use std::fmt::*;
use std::str::*;
use std::cmp::*;
use std::collections::*;

fn getline() -> String{
    let mut res = String::new();
    std::io::stdin().read_line(&mut res).ok();
    res
}

macro_rules! readl {
    ($t: ty) => {
        {
            let s = getline();
            s.trim().parse::<$t>().unwrap()
        }
    };
    ($( $t: ty),+ ) => {
        {
            let s = getline();
            let mut iter = s.trim().split(' ');
            ($(iter.next().unwrap().parse::<$t>().unwrap(),)*) 
        }
    };
}

macro_rules! readlvec {
    ($t: ty) => {
        {
            let s = getline();
            let iter = s.trim().split(' ');
            iter.map(|x| x.parse().unwrap()).collect::<Vec<$t>>()
        }
    }
}

macro_rules! mvec {
    ($v: expr, $s: expr) => {
        vec![$v; $s]
    };
    ($v: expr, $s: expr, $($t: expr),*) => {
        vec![mvec!($v, $($t),*); $s]
    };
}

macro_rules! debug {
    ($x: expr) => {
        println!("{}: {:?}", stringify!($x), $x)
    }
}

fn printiter<'a, T>(v: &'a T)
where
    &'a T: std::iter::IntoIterator, 
    <&'a T as std::iter::IntoIterator>::Item: std::fmt::Display {
    for (i,e) in v.into_iter().enumerate() {
        if i != 0 {
            print!(" ");
        }
        print!("{}", e);
    }
    println!("");
}

struct ContestPrinter {
    s: String,
}

impl ContestPrinter {
    fn new() -> ContestPrinter {
        ContestPrinter {
        s: String::new(),
        }
    }

    fn print<T>(&mut self, x: T)
        where T: std::fmt::Display {
        self.s.push_str(format!("{}", x).as_str());
    }

    fn println<T>(&mut self, x: T)
        where T: std::fmt::Display {
        self.s.push_str(format!("{}\n", x).as_str());
    }
}

impl std::ops::Drop for ContestPrinter {
    fn drop(&mut self) {
        print!("{}", self.s);
    }
}

fn is_max_i64(num: i64) -> bool { if num == i64::max_value() { true } else { false } }

// 重さの配列, 欲しい和, あり得る最大の和 -> 欲しい和を作れるか
fn knapsack_equal(ws: &Vec<usize>, sum: usize, possible_sum: usize) -> bool {
    let possible_sum = 100 * 100 + 1;
    let N1 = ws.len() + 1;
    let mut dp = vec![vec![false; possible_sum]; N1];
    dp[0][0] = true;
    for i in 1..N1 {
        let w = ws[i-1];
        for j in 0..possible_sum {
            if j >= w {
                dp[i][j] = dp[i - 1][j] | dp[i - 1][j - w];
            } else {
                dp[i][j] = dp[i - 1][j];
            }
        }
    }
    dp[N1-1][sum]
}

fn main() {
    let mut pr = ContestPrinter::new();
    
    let N = readl!(usize);
    let N1 = N + 1;
    let mut dp: Vec<Vec<i64>> = vec![vec![0; N1]; N1];
    dp[0][0] = 1;

    for i in 1..N1 {
        for j in 1..N1 {
            dp[i][j] = dp[i-1][j - 1] + if j > 1 { dp[i-1][j - 2] } else { 0 };
        }
    }

    let mut ans = 0;
    for i in 0..N1 {
        ans += dp[i][N];
    }
    pr.println(ans);
}