# include <iostream>
# include <algorithm>
# include <vector>
# include <string>
# include <set>
# include <map>
# include <cmath>
# include <iomanip>
# include <functional>
# include <utility>
# include <stack>
# include <queue>
# include <list>
# include <bitset>
# include <complex>
# include <numeric>
# include <tuple>
using namespace std;
using LL = long long;
using ULL = unsigned long long;
constexpr int INF = 2000000000;
constexpr int HINF = INF / 2;
constexpr double DINF = 100000000000000000.0;
constexpr long long LINF = 9223372036854775807;
constexpr long long HLINF = 4500000000000000000;
const double PI = acos(-1);
int dx[4] = { 0,1,0,-1 }, dy[4] = { 1,0,-1,0 };
#define ALL(x)    (x).begin(),(x).end()
#define UNIQ(c)   (c).erase(unique(ALL((c))), end((c)))
#define mp        make_pair
#define eb        emplace_back
typedef pair<LL, double> P;
typedef pair<P, P> PP;

LL dp[60];
int main() {
	int n;
	cin >> n;
	dp[0] = 1;
	for (int i = 1; i <= n; i++) {
		dp[i] += dp[i - 1];
		if(i!=1)dp[i] += dp[i - 2];
	}
	cout << dp[n] << endl;
}