#include <cstdio>
FILE *f=fopen("nunta.in","r");
FILE *g=fopen("nunta.out","w");
short a[250],b[250],c[250];
short n,i,j;

int main()
{
    fscanf(f,"%d",&n);
    if (n<=3){
        fprintf(g,"%d",n);;
        return 0;
    }
    a[0]=1;a[1]=2;
    b[0]=1;b[1]=3;
    for (i=4;i<=n;i++) {
        c[0]=b[0];
        for (j=1;j<=c[0];j++) {
            c[j]+=a[j]+b[j];
            if (c[j]>9) {
                c[j+1]+=c[j]/10;
                c[j]%=10;
            }
        }
        if (c[c[0]+1])
            c[0]++;

        for (j=c[0];j>=0;j--)
            a[j]=b[j],b[j]=c[j],c[j]=0;

    }
    for (i=b[0];i>=1;i--)
        fprintf(g,"%c",b[i]+'0');
    return 0;
}