010：计算球的体积

//斐波那契数列
#include<iostream>
using namespace std;
int main()
{
    int n1 = 1,n2 = 1,k,num;
    cin >> k;
    if(k == 1 || k == 2)
        cout << 1;
    else
    {
        for(int i = 3;i <= k;i++)
        {
            num = n1 + n2;
            n1 = n2;
            n2 = num;
        }
        cout << num;
    }
    return 0;
}

//求阶乘的和，解法1，一般思路
#include<iostream>
using namespace std;
int main()
{
    int n,n1 = 1,n2 = 0;
    cin >> n;
    for(int i = 1;i <= n;i++)
    {
        n1 = 1;
        for(int j = 1;j <= i;j++)
        {
            n1 *= j;
        }
        n2 += n1;
    }
    cout << n2;
    return 0;
}
//解法2，更快的解法
#include<iostream>
using namespace std;
int main()
{
    int n;
    cin >> n;
    int sum = 0;
    int factorial = 1;
    for(int i = 1;i <= n;++i){
        factorial *= i;
        sum += factorial;
    }
    cout << sum;
    return 0;
}