Palindrome Missing Alphabet

String S which is a palindrome is passed as the input. But just one alphabet A is missing in S. The program must print the missing alphabet A.

Note: The FIRST alphabet of S will always be present.

Input Format:
The first line contains S.

Output Format:
The first line contains the missing alphabet A.

Boundary Conditions:
The length of the input string S is between 3 to 100.
The FIRST alphabet of S will always be present.

Example Input/Output 1:
Input:
malayaam
Output:
l

Example Input/Output 2:
Input:
abcddcb
Output:
a

Program
#include<stdio.h>
#include <stdlib.h>

int main()
{
   char S[100];
   int i,j,a;
   scanf("%s",S);
   a=strlen(S);
   if (S[0]!=S[a-1])
   {
         printf("%c",S[0]);
         exit(0);
   }
   for(i=0,j=a-1;i<a/2;i++,j--)
   {
       if (S[i]!=S[j])  
       {
          if (S[i+1]==S[j])
                   printf("%c",S[i]);
           else
                  printf("%c",S[j]);
           break;
         }
  }     
}

OUTPUT
malayaam
l