题解 | 斐波那契数列

import java.util.Scanner;

public class Main {

    private static final int MOD = 1000000007;

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int k = in.nextInt();
        System.out.println(fS(k));
        in.close();
    }

    public static int fS(int F) {
        if (F == 1 || F == 2) {
            return 1;
        }
        int a = 1; 
        int b = 1; 
        for (int i = 3; i <= F; i++) {
            int c = (a + b) % MOD;// 每次计算都取模，防止溢出
            a = b;
            b = c;
        }
        return b;
    }
}