#include<fstream>
using namespace std;
ifstream f("nunta.in");
ofstream g("nunta.out");
long long a,b,c,n,i;
int main()
{f>>n;
a=1;b=1;
for(i=1;i<n;++i)
{c=a+b;
a=b;
b=c;
}
g<<c<<'\n';
f.close();
g.close();
return 0;
}