#include <fstream>

using namespace std;
struct vec
{
    int l;
    char c[210];
};
vec a,b,C,nul;
int n;
vec sum(vec A, vec B)
{
    C=nul;
    char x=0;
    C.l=max(A.l,B.l);
    for(int i=1; i<=C.l; i++)
    {
        C.c[i]=A.c[i]+B.c[i]+x;
        x=C.c[i]/10;
        C.c[i]%=10;
    }
    if(x)
    {
        C.l++;
        C.c[C.l]=x;
    }
    return C;
}
int main()
{
    ifstream f("nunta.in");
    ofstream g("nunta.out");
    f>>n;
    a.l=1;
    a.c[1]=1;
    b.l=1;
    b.c[1]=0;
    while(n--)
    {
        b=sum(a,b);
        swap(a,b);
    }
    for(int i=a.l; i; i--)
    {
        g<<(int)a.c[i];
    }
    g<<'\n';
    f.close(); g.close();
    return 0;
}