#include <bits/stdc++.h>
#define up(r,l,i) for(int i=r;i<=l;i++)
#define dn(r,l,i) for(int i=r;i>=l;i--) 
using namespace std;
int n;
int c[1000], a[1000], b[1000],len;
void supperAdd(int x[], int y[]) {
	memset(c, 0, 1005);
	up(1, sizeof(b) / sizeof(b[0]), i) {
		c[i] += a[i] + b[i];
		c[i + 1] = c[i] / 10;
		c[i] = c[i] % 10;
	}
}
int main()
{
	cin >> n;
	a[1] = 1;
	b[1] = 2;
	len = 1;
	up(3, n, i) {
		supperAdd(a, b);
		memcpy(a, b, sizeof(b) / sizeof(b[0]));
		memcpy(b, c, sizeof(c) / sizeof(c[0]));
	}
	
	len = 999;
	while (c[len] == 0 && len > 1) len--;
	dn(len, 1, i) {
		cout << c[i];
	}
	return 0;
}