题解 | #跳台阶#

#include <iostream>
using namespace std;

// F(i) = F(i-1) + F(i-2)
// F(0) = 0; F(1) = 1; F(2) = 2;
int main() {
    int n = 0;
    int first = 1;
    int second = 2;
    int third;
    int res;

    scanf ("%d", &n);
    if (n < 1)
    {
        res = 0;
    }
    else {
        for (int i = 2; i <= n; i++)
        {
            third = first + second;
            first = second;
            second = third;
        }
        res = first;
    }

    printf("%d", res);
    return 0;
}