#include <iostream>
#include <vector>
#include <algorithm>
#include <map>
#include <string>
#include <queue>
#include <stack>
#include <math.h>
#include <set>
#define ALL(obj) (obj).begin(),(obj).end()
#define RALL(obj) (obj).rbegin(),(obj).rend()
#define P pair<int, int>

#define MOD 1000000007
#define INF 1012345678
#define NINF (-2147483647-1)
#define LLINF 9223372036854775807
using ll = long long;
using namespace std;

int main() {
    int N;
    cin >> N;
    vector <ll> dp(N + 1, 0);
    dp[0] = 1;
    for (int i = 0; i < N; i++)
    {
        dp[i + 1] += dp[i];
        if (i < N - 1) {
            dp[i + 2] += dp[i];
        }
    }
    cout << dp[N] << endl;
    getchar(); getchar();
    return 0;
}