so easy

#include<bits/stdc++.h>
using namespace std;
long long a[10000] ={0,1,2,0},n;
int main(){
cin>>n;
for( int i =3;i<= 100;i++){
a[i] =a[i-1] + a[i-2];
}
cout<<a[n];

return 0;

}