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#include <iostream>
#include <fstream>
#include <math.h>
#include <iomanip>
#include <cmath>
#include <vector>
int recursion(int a) {
	if (a > 0) return recursion(a - 1) + recursion(a - 2);
	else return 1;
}
int main() {
	int a; std::cin >> a;
	std::cout << recursion(a);
}