include <bits/stdc++.h>

using namespace std; long long a[100];

int main() {

a[0] = 1;
a[1] = 1;
int n;
cin >> n;
for (int i = 2; i <= n; i++) {
	a[i] = a[i - 1] + a[i - 2];
}
cout << a[n];
return 0;

}