/ java 大整数类
n大小在20以内计算，20以外直接输出
/

import java.util.;
import java.math.;
public class _3177 {
public static void main(String[] args){

Scanner scanner = new Scanner(System.in);
BigInteger a = new BigInteger("1");
BigInteger b = new BigInteger("1");

int n = scanner.nextInt();
if(n<20){
    for(int i = 1; i < n; i++){
        BigInteger c = a.add(b);
        a = b;
        b = c;
    }
    BigDecimal c = new BigDecimal(a);
    BigDecimal d = new BigDecimal(b);
    System.out.print(c.divide(d,8,BigDecimal.ROUND_HALF_UP));//保留8位，向上取整
}
else {
    System.out.print("0.61803399");
}

}
}