#include <stdio.h>

int main(void)
{
	int N;
	scanf("%d", &N);
	int i;
	long fibonacci[] = { 1, 1, 2 };
	for (i = 3; i < N + 1; ++i) {
		int j;
		for (j = 0; j < 2; ++j) fibonacci[j] = fibonacci[j + 1];
		fibonacci[2] = fibonacci[0] + fibonacci[1];
	}
	if (N == 1) printf("%ld", fibonacci[1]);
	else printf("%ld", fibonacci[2]);
	return 0;
}