#include <cstdio>
#include <iostream>
#include <sstream>
#include <fstream>
#include <iomanip>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <bitset>
#include <numeric>
#include <limits>
#include <climits>
#include <cfloat>
#include <functional>
using namespace std;

int main()
{
    int n;
    cin >> n;

    vector<long long> dp(n+1, 0);
    dp[0] = 1;
    for(int i=0; i<n; ++i){
        dp[i+1] += dp[i];
        if(i+2 <= n)
            dp[i+2] += dp[i];
    }
    cout << dp[n] << endl;

    return 0;
}