#include<stdio.h>
int n;
void Rezolvare(){
    int i,a=1,b=2,aux;
    scanf("%d",&n);
    for(i=3; i<=n; ++i){
        aux=a+b;
        a=b;
        b=aux;}
    if(n==1)
        printf("1");
    else if(n==2)
        printf("2");
    else
        printf("%d",b);}
int main(){
    freopen("nunta.in","r",stdin);
    freopen("nunta.out","w",stdout);
    Rezolvare();
    return 0;}