#include <cstdio>
#include <cstdlib>
#include <iostream>
#include <cstring>
#include <string>
#include <algorithm>
#include <cmath>
#include <vector>
#include <queue>
#include <stack>
#include <deque>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <functional>

typedef long long int ll;
using namespace std;
#define INF 1234567890
#define N 200000

const int LIMIT = 1e+9;
int n, m;

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

	cin >> n;
	ll a = 0, b = 1;
	while (n--) {
		b += a;
		a = b - a;
	}
	cout << a;

	return 0;
}