#include <iostream>
using namespace std;

long long f(long long n,long long last,long long now,long long cnt)
{
    if(cnt == n)
    return now;
    return f(n,now,last+now,cnt+1);
}

int main()
{
    int n;
    cin >> n;
    cout << f(n,1,1,1) << endl;
    
    return 0;
}