#include<bits/stdc++.h>
#define rep(i,n,m) for(int i = (n); i <(m); i++)
#define rrep(i,n,m) for(int i = (n) - 1; i >=(m); i--)
using namespace std;
using ll = long long;

int main()
{
    int n;
    cin >> n;
    vector<int> dp(n+2, 0);
    dp[0] = 1;
    rep(i, 0, n)
    {
        dp[i+1] += dp[i];
        dp[i+2] += dp[i];
    }
    cout << dp[n] << endl;
    return 0;
}