A8340 | Lucky Substring
时间限制1s
内存限制256MB
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题目描述
Petya loves lucky numbers. Everybody knows that lucky numbers are positive integers whose decimal representation contains only the lucky digits 4 and 7. For example, numbers 47, 744, 4 are lucky and 5, 17, 467 are not.
One day Petya was delivered a string $s$ , containing only digits. He needs to find a string that
- represents a lucky number without leading zeroes,
- is not empty,
- is contained in $s$ as a substring the maximum number of times.
Among all the strings for which the three conditions given above are fulfilled, Petya only needs the lexicographically minimum one. Find this string for Petya.
One day Petya was delivered a string $s$ , containing only digits. He needs to find a string that
- represents a lucky number without leading zeroes,
- is not empty,
- is contained in $s$ as a substring the maximum number of times.
Among all the strings for which the three conditions given above are fulfilled, Petya only needs the lexicographically minimum one. Find this string for Petya.
输入格式
The single line contains a non-empty string $s$ whose length can range from $1$ to $50$ , inclusive. The string only contains digits. The string can contain leading zeroes.
输出格式
In the only line print the answer to Petya's problem. If the sought string does not exist, print "-1" (without quotes).
输入输出样例
输入 #1
047
输出 #1
4
输入 #2
16
输出 #2
-1
输入 #3
472747
输出 #3
7
The lexicographical comparison of strings is performed by the < operator in the modern programming languages. String $x$ is lexicographically less than string $y$ either if $x$ is a prefix of $y$ , or exists such $i$ ( $1<=i<=min(|x|,|y|)$ ), that $x_{i}<y_{i}$ and for any $j$ ( $1<=j<i$ ) $x_{j}=y_{j}$ . Here $|a|$ denotes the length of string $a$ .
In the first sample three conditions are fulfilled for strings "4", "7" and "47". The lexicographically minimum one is "4".
In the second sample $s$ has no substrings which are lucky numbers.
In the third sample the three conditions are only fulfilled for string "7".
In the first sample three conditions are fulfilled for strings "4", "7" and "47". The lexicographically minimum one is "4".
In the second sample $s$ has no substrings which are lucky numbers.
In the third sample the three conditions are only fulfilled for string "7".
C++ 编辑器
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输出
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评测结果：Accepted