#include<iostream>
#include<cstdio>
#include<fstream>
#include<algorithm>
#include<cmath>
#include<deque>
#include<vector>
#include<queue>
#include<string>
#include<cstring>
#include<map>
#include<stack>
#include<set>
using namespace std;
long long f(long long n) 
{
	if (n == 1) return 1;
	if (n == 2) return 2;
	return f(n-1) + f(n-2);
}
int main()
{
	long long n;
	cin>>n;
	cout<<f(n);
}

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