本人第一次一次AC啊~~~~泪奔
用了二分搜索法，设了一些哨兵，为了提高速度。
代码如下：

#include<stdio.h>
#include<string.h>

double result[277];
int flag[7];
void init(void);
main()
{
	char word[100000][4];
	unsigned long int total;
	unsigned long int i=0;
	double wordNum;
	int pos;
	int high,low,mid;

	init();

	while(1)
	{
		scanf("%s",word[i]);
		if(strcmp(word[i],"0.00") == 0)
			break;
		i++;
	}
	total = i;

	for(i=0;i<total;i++)
	{
		wordNum = (word[i][0] - '0') * 1.0 + (word[i][2] - '0') * 0.1 + (word[i][3] - '0') * 0.01;
		pos = (int)wordNum;
		if(result[flag[pos]] < wordNum)
		{
			low = flag[pos];
			high = flag[pos+1];
		}
		else
		{
			low = flag[pos-1];
			high = flag[pos];
		}

		while(1)
		{
			if((high == (low + 1)) && result[low] < wordNum && result[high] >= wordNum)
			{
				printf("%d card(s)\n",high);
				break;
			}
			mid = (high + low)/2;
			if(result[mid] < wordNum)
				low = mid;
			else
				high = mid;
		}
	}
	
	
	
}

void init()
{
	int i=0;
	double sum = 0;
	int initFlag = 1;
	flag[0] = 0;
	result[0] = 0.0;
	while(sum <= 5.20)
	{
		i++;
		sum += 1.0/(i+1);
		result[i] = sum;
		if(sum >= initFlag)
		{
			flag[initFlag] = i;
			initFlag++;
		}
	}
	flag[6] = 276;
}