#include<stdio.h>
int n,a[1001],b[1001];
void adun(){
    int i,aux,t=0;
    for(i=1; i<=b[0]; ++i){
        aux=b[i];
        b[i]=(a[i]+aux+t)%10;
        t=(a[i]+aux)/10;
        a[i]=aux;}
    if(t)
        b[++b[0]]=t;}
void solve(){
    int i;
    scanf("%d",&n);
    b[0]=1;
    a[1]=1;
    b[1]=2;
    if(n==1)
        printf("1");
    else if(n==2)
        printf("2");
    else{
        for(i=3; i<=n; ++i)
            adun();
        for(i=b[0]+1; i>0; --i){
            while(!b[i])
                --i;
            printf("%d",b[i]);}}}
int main(){
    freopen("nunta.in","r",stdin);
    freopen("nunta.out","w",stdout);
    solve();
    return 0;}