#include <bits/stdc++.h>
using namespace std;
int num(int n){
    int r;
    if(n==1||n==2){
        r=1;
    }
    else{
        r=num(n-1)+num(n-2);
    }
    return r;
}
int main(){
    int v;
    cin>>v;
    cout<<num(v);
    return 0;
}

/**************************************************************
	Problem: 1238
	User: luyanchen
	Language: C++
	Result: Accepted
	Time:16 ms
	Memory:2072 kb
****************************************************************/