#include <fstream.h>
int main ()
{ int n,a,b,c,i,k;
ifstream f("nunta.in");
ofstream g("nunta.out");
f>>n;
if (n==1) g <<"1";
else if (n==2) g <<"1";
else {    a=1; b=2; 
	      for (i=3;i<=n;i++) {
                        c=a+b;
                        a=b;
			b=c; 
			 } 
		  g<<c;
}
f.close();
g.close();
return 0;
}