#include<bits/stdc++.h>
using namespace std;

typedef long long LL;
int n;
LL dp[30];
int main()
{
    dp[1] = 1, dp[2] = 2;
    for(int i = 3; i <= 20; i ++)
        dp[i] = dp[i - 1] + dp[i - 2];
        
    while(cin >> n)
    {
        cout << dp[n] << endl;
    }
    
    return 0;
}