#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define llong long long

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

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