#include <iostream>
#include <cstdio>
#include <string>
#include <vector>
#include <map>
#include <algorithm>
#include <set>
#include <bitset>

using namespace std;

int main() {
	int n;
	cin >> n;
	vector <int> fb(n + 1);
	fb[0] = 0;
	fb[1] = 1;
	for(int i = 2; i <= n; i++){
		fb[i] = fb[i - 1] + fb[i - 2];
	}
	cout << fb[n - 1];

}