#include "bits/stdc++.h"

using namespace std;

using ll = long long;
using ld = long double;

const double PI = 3.1415926535897932384626433832795;

const int dx[] = { 0, 1, 0, -1 };
const int dy[] = { -1, 0, 1, 0 };

int gcd(int x, int y) { return y ? gcd(y, x % y) : abs(x); }
ll gcd(ll x, ll y) { return y ? gcd(y, x % y) : abs(x); }
int lcm(int x, int y) { return x / gcd(x, y) * y; }
ll lcm(ll x, ll y) { return x / gcd(x, y) * y; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(0);

	ll n;
	cin >> n;

	vector<ll> dp(n + 1);
	dp[1] = 1;
	dp[2] = 2;
	for (ll i = 3; i < dp.size(); i++) {
		dp[i] = dp[i - 2] + dp[i - 1];
	}

	cout << dp[n] << endl;
	return 0;
}