#include<iostream> using namespace std; int main(){ int a,j=0,k=1; cin>>a; //j = 0 ---0 //k = 1 ---1 //1 //j = 1 ---2 //k = 2 ---3 //2 //j = 3 ---4 //k = 5 ---5 //3 //j = 8 ---6 //k = 13 ---7 //4 //j = 21 ---8 //k = 44 ---9 for(int i=0;i<a/2;i++){ j+=k; k+=j; } if(a%2==1){ cout<<k; } else{ cout<<j; } }