#include <iostream>
int main() {
int n;
std::cin >> n;
if (n > 20) {
printf("0.61803399\n");
return 0;
}
int a = 0;
int b = 1;
int c;
while (n--) {
c = a + b;
a = b;
b = c;
}
printf("%.8f\n", 1.0 * a / b);
return 0;
}
n>20这样算取巧嘛,请问有什么数学方法能算嘛