#include <fstream>

using namespace std;

ifstream f("nunta.in");
ofstream g("nunta.out");

unsigned long long fib[1000];
int n, i;

int main() {
    f >> n; fib[1] = 1, fib[2] = 2;
    for (i = 3; i <= n; i++) fib[i] = fib[i-1]+fib[i-2];
    g << fib[n];
}