PAT A1031 Hello World for U(gcc에서 gets()는 error)

1031 Hello World for U(20)(20점)
Given any string of N (>=5) characters, you are asked to form the characters into the shape of U. For example, "helloworld"can be printed as:

h  d
e  l
l  r
lowo

That is, the characters must be printed in the original order, starting top-down from the left vertical line with n~1~ characters, then left to right along the bottom line with n~2~ characters, and finally bottom-up along the vertical line with n~3~ characters. And more, we would like U to be as squared as possible -- that is, it must be satisfied that n~1~ = n~3~ = max { k| k <= n~2~ for all 3 <= n~2~ <= N } with n~1~

n~2~ + n~3~ - 2 = N.

Input Specification:
Each input file contains one test case. Each case contains one string with no less than 5 and no more than 80 characters in a line. The string contains no white space.
Output Specification:
For each test case, print the input string in the shape of U as specified in the description.
Sample Input:

helloworld!

Sample Output:

h   !
e   d
l   l
lowor

#include 
#include 

int main(){
	int n1,n2,nn;
		
	char str[100];
	scanf("%s",&str);
	int N = strlen(str);
	n1 = (N+2)/3;
	n2 = (N+2)/3;
	nn = N-n1-n2;
	
	for(int i=0;i