#include <iostream>
#include <fstream>
#include <vector>
#define MAXN 100

using namespace std;

ifstream in("fib.in");
ofstream out("fib.out");


long int PD(int n) {
    long int D[n+1] = {0};
    if (n <= 1) {
        return n;
    }
    if (D[n] == 0) {
        D[n] = PD(n-1) + PD(n-2);
    }
    return D[n];
}

int main()
{
    long int n;
    in>>n;
    out<<PD(n);
    return 0;
}