#include <stdio.h>

FILE * fin;
FILE * fout;

char a[10], b[10], c[10];
int n,s,t;

int main()
{
	int i;

	fin = fopen("nunta.in", "r");
	fout = fopen("nunta.out", "w");
	fscanf(fin, "%d", &n);
	if (n < 3) fprintf(fout, "%d\n", n);
	else
	{
		a[0] = b[0] = a[1] = 1;
		b[1] = 2;
		while (n-- >= 3)
		{
			c[0] = b[0];
			for (i = 1; i <= b[0]; i++)
			{
				s = a[i] + b[i] + t;
				c[i] = s % 10;
				t = s / 10;
			}
			while (t)
			{
				c[++c[0]] = t % 10;
				t /= 10;
			}
			for (i = 0; i <= b[0]; i++)
				a[i] = b[i];
			for (i = 0; i <= c[0]; i++)
				b[i] = c[i];
		}
		for (i = c[0]; i >= 1; i--)
			fprintf(fout, "%d", c[i]);
		fprintf(fout, "\n");
	}
	return 0;
}