#include <fstream>
using namespace std;
ifstream fin("nunta.in");
ofstream fout("nunta.out");
int n,i,d[1000];
int main(){
    fin>>n;
    d[1]=1;d[2]=2;d[3]=3;
    for(i=4;i<=n;i++)
        d[i]=d[i-1]+d[i-2];
    fout<<d[n];
    return 0;
}