https://www.acmicpc.net/problem/2748
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
int n = sc.nextInt();
long num1 = 0;
long num2 = 1;
for (int i = 0; i < n; i++) {
long sum = num1 + num2;
num1 = num2;
num2 = sum;
}
System.out.println(num1);
}
}