分别用while语句、do-while语句、for语句编写程序， 计算e≈1+1/1!+1/2!+...+1/n!

以下是三种不同的方法来计算e≈1+1/1!+1/2!+...+1/n!：
1. 使用while循环来计算

n = int(input())
jie = 1
sum = 0
i = 1
while n >= i:
    jie = jie * i
    sum = sum + jie
    i = i + 1
print(sum)

2. 使用do-while循环来计算

public class Example1_3 {
    public static void main(String args[]) {
        double a = 1, b = 1, c = 0;
        System.out.println("do-while循环:");
        do {
            c = b + c;
            a++;
            b = (1.0 / a) * b;
        } while (a <= 20);
        System.out.println(" " + c);
        System.out.println("for循环:");
    }
}

3. 使用for循环来计算

public class Example1_3 {
    public static void main(String args[]) {
        double a, b, c;
        System.out.println("for循环:");
        for (c = 0, b = 1, a = 1; a <= 20; a++) {
            b *= (1.0 / a);
            c += b;
        }
        System.out.println(" " + c);
    }
}