#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, x, n) for (int i = x; i < (n); i++)
#define ALL(n) begin(n), end(n)
template <class T>
inline bool chmax(T& a, T b) {
    if (a < b) {
        a = b;
        return 1;
    }
    return 0;
}
template <class T>
inline bool chmin(T& a, T b) {
    if (a > b) {
        a = b;
        return 1;
    }
    return 0;
}
const long long INF = numeric_limits<long long>::max();
using Graph = vector<vector<int> >;
int main() {
    int n;
    cin >> n;

    ll dp[100010];
    dp[0] = 0;
    dp[1] = 1;
    dp[2] = 2;
  	dp[3] = 3;
    rep2(i, 4, n + 1) { dp[i] = dp[i - 1] + dp[i - 2]; }

    cout << dp[n];
}