#include <stdio.h>
long long n,p,a,c,i;
FILE *in=fopen("date.in","rt"),*out=fopen("date.out","wt");

int main( )
{
    fscanf(in,"%lld",&n);
   p=1;
   a=1;
   for(i=2;i<=n+1;i++)
    {
    c=p+a;
    a=p;
    p=c;
    }
    fprintf(out,"%lld",c);
    return 0;
}