#include <cstdio>
#include <fstream>
using namespace std;
unsigned char a[212], b[212];
void add(unsigned char f1[], unsigned char f2[])
{
    int i, t=0;
    for(i=1; i<=f1[0] || t!=0; i++)
    {
        f2[i]+=t+f1[i];
        t=f2[i]/10;
        f2[i]%=10;
    }
    f2[0]=i-1;
}
int main()
{
    int n, i;
    FILE *fin=fopen("nunta.in", "r");
    FILE *fout=fopen("nunta.out", "w");
    fscanf(fin, "%d", &n);
    a[0]=1, a[1]=1, b[0]=1, b[1]=2;
    for(i=3; i<=n; i++)
        if(i%2) add(b,a);
        else add(a,b);
    if(n%2)
    {
        for(i=a[0]; i>=1; i--)
            fputc(char(a[i]+'0'),fout);
    }
    else
    {
        for(i=b[0]; i>=1; i--)
            fputc(char(b[i]+'0'),fout);
    }
    return 0;
}