#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define F first
#define S second
#define pii pair<int, int>
#define eb emplace_back
#define all(v) v.begin(), v.end()
#define rep(i, n) for (int i = 0; i < n; ++i)
#define rep3(i, l, n) for (int i = l; i < n; ++i)
#define chmax(a, b) a = max(a, b)
#define chmin(a, b) a = min(a, b)
#define out(a) cout << a << endl
#define SZ(v) (int)v.size()
#define inf (int)(1e9+7)
int main() {
    int n; cin >> n;
    ll dp[n + 1]; fill_n(dp, n + 1, 0);
    dp[1] = 1;
    dp[2] = 2;
    rep3(i, 3, n + 1) {
        dp[i] = dp[i - 1] + dp[i - 2];
    }
    out(dp[n]);
}