#include <fstream>

using namespace std;

ifstream fin ("nunta.in");
ofstream fout ("nunta.out");

int n, i, d[3][10],j,t,maxim;

void suma (int x, int y ,int z ) {

     maxim=d[x][0];

    if (d[y][0]>maxim)
        maxim=d[y][0];
    for (int i=1;i<=maxim;i++) {
        d[z][i]=d[x][i]+d[y][i]+t;
        t=d[z][i]/10;
        d[z][i]%=10;
    }
    d[z][0]=maxim;
    if (t!=0)
        d[z][++d[z][0]]=t;
}

int main () {

    fin>>n;
    d[0][0]=d[0][1]=d[1][0]=1;
    d[1][1]=2;
    for (i=3;i<=n;i++){
        suma (0,1,2);
        for (j=0;j<=d[1][0];j++)
            d[0][j]=d[1][j];
        for (j=0;j<=d[2][0];j++)
            d[1][j]=d[2][j];
    }
    for (i=d[2][0];i>=1;i--)
        fout<<d[2][i];


    return 0;
}