#include<cstdio>
using namespace std;
FILE *fin= fopen("nunta.in", "r");
FILE *fout= fopen("nunta.out", "w");
int n,a,b,c,i;
int main(){
    fscanf(fin, "%d" ,&n);
    if(n==1){
        fprintf(fout, "1");
        return 0;
    }
    else{
        if(n==2){
            fprintf(fout, "2");
            return 0;
        }
        else{
            a=1;
            b=2;
            c=a+b;
            for(i=4;i<=n;i++){
                a=b;
                b=c;
                c=a+b;
            }
            fprintf(fout,"%d",c);
        }
    }
    return 0;
}