SGU107 - 987654321 problem

107. 987654321 problem

time limit per test: 0.5 sec. 
memory limit per test: 4096 KB

 

For given number N you must output amount of N-digit numbers, such, that last digits of their square is equal to 987654321.

 

Input

Input contains integer number N (1<=N<=10⁶)

 

Output

Write answer to the output.

 

Sample Input

8

Sample Output

0

题解：用枚举显然超时。只能用观察法了。小于八位的情况数为0，九位有8种情况，当N>9时，九位以上的数字对于后九位都是没有影响的，所以最高位有9种取法，其余大于九位的都是10种取法。然后运用乘法原理得出最终答案。

#include<stdio.h>
int main(void)
{
    int n,i;
    scanf("%d",&n);
    if(n<=8) printf("0\n");
    else
    if(n==9) printf("8\n");
    else
    {
        printf("72");
        for(i=11;i<=n;i++)
        printf("0");
        printf("\n");
    }
    return 0;
}