#include <stdio.h>

int n;
int A[1000], B[1000];

void add(int A[], int B[])
{
    int i, t=0;
    for (i=1; i<=A[0] || i<=B[0] || t; ++i, t/=10)
	A[i]=(t+=A[i]+B[i])%10;
    A[0]=i-1;
}

int main()
{
    freopen("nunta.in","r",stdin);
    freopen("nunta.out","w",stdout);

    scanf("%d", &n);
    int i;

    A[0]=1;A[1]=1;
    B[0]=1;B[1]=2;
    for (i=3; i<=n; ++i) 
	if (i&1) add(A,B);
	else add(B,A);

    if (n&1) 
	for (i=A[0]; i>=1; --i) 
	    printf("%d", A[i]);
    else 
	for (i=B[0]; i>=1; --i)
	    printf("%d", B[i]);

    return 0;
}