#include <iostream>
#include <vector>
#include <string>
#include <cstring>
#include <math.h>
#include <cmath>
#include <limits.h>
#include <map>
#include <unordered_map>
#include <set>
#include <queue>
#include <algorithm>
#include <functional>
#include <stdio.h>
using namespace std;

long long MOD = 1000000007;

int main() {

    int N;
    cin >> N;

    long long dp[N+2] = {0};
    dp[0] = 1;

    for ( int i = 0; i < N; i++ ) {
        dp[i+1] += dp[i];
        dp[i+2] += dp[i];
    }

    cout << dp[N] << endl;

    return 0;
}