#include <iostream>
using namespace std;
typedef long long ll;
int N;
ll dp[60];
int main(void){
    // Your code here!
    int N;
    cin >> N;
    for(int i = 0; i < 60; i++) dp[i] = 0;
    dp[0] = 1;
    
    for(int i = 0; i < 50; i++){
        dp[i+1] += dp[i];
        dp[i+2] += dp[i];
    }
    
    cout << dp[N] << endl;
}