#include <iostream>
#include <math.h>
#include <iomanip>
using namespace std;
int main()
{
    int n;
    cin >> n;
    int a,b,c;
    a = b = c = 1;
    for(int i = 3; i <= n ; ++i)
    {
    	c = a + b;
    	a = b;
    	b = c;
	}
	cout << c << endl;   
}

#include <stdio.h>
#include <iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    int a,b,c;
    a = b = c = 1;
    for (int i = 3;i<= n; i++)
    {
        c = a + b;
        a = b;
        b = c;
    }
    cout << c << endl;
}