#include <iostream>
#include <vector>
#include <string>
#include <stack>
#include <queue>
#include <deque>
#include <set>
#include <map>
#include <algorithm>	// require sort next_permutation count __gcd reverse etc.
#include <cstdlib>	// require abs exit atof atoi 
#include <cstdio>		// require scanf printf
#include <functional>
#include <numeric>	// require accumulate
#include <cmath>		// require fabs
#include <climits>
#include <limits>
#include <cfloat>
#include <iomanip>	// require setw
#include <sstream>	// require stringstream 
#include <cstring>	// require memset
#include <cctype>		// require tolower, toupper
#include <fstream>	// require freopen
#include <ctime>		// require srand
#define rep(i,n) for(int i=0;i<(n);i++)
#define ALL(A) A.begin(), A.end()

/*
	No.44 DPなすごろく

	DP解：

	dp[0] = 1;
	dp[1] = 1;
	dp[i] = dp[i-1] + dp[i-2];（フィボナッチ数列）
*/
using namespace std;

typedef long long ll;
typedef pair<int, int> P;

const int MAX_N = 55;

ll dp[MAX_N];

int main()
{
	memset (dp, 0LL, sizeof (dp ) );
	ios_base::sync_with_stdio(0);
	int N; cin >> N;
	
	dp[0] = 1LL;
	dp[1] = 1LL;

	for (int i = 2; i <= N; i++ ){
		dp[i] = dp[i-1] + dp[i-2];
	} // end for
	
	cout << dp[N] << endl;

	return 0;
}