include
using namespace std;
int main() {
int n;
cin >> n;
if (n == 1 || n == 2) {
cout << 1 << endl;
return 0;
}
int a = 1, b = 1; // f(1), f(2)
int ans;
for (int i = 3; i <= n; i++) {
ans = a + b;
a = b;
b = ans;
}
cout << ans << endl;
return 0;
}