Please help me, I can't find error in my program, but WA4

#include<iostream.h>
#include<stdlib.h>
#include<string.h>
#define SIZE 10000
int main() {
    char s1[SIZE], *s2;

    int i, k, t, j, done;

    cin >> s1;
    s2 = (char*) calloc (strlen (s1)+1, sizeof(char));

    k = strlen (s1) - 1;


    for (i = k; i >= 0; i--)
        s2[i] = s1[k - i];

    done = 0;

    for (i = 0; i <= k; i++) {
        for (j = i; j <= k; j++) {
            if ( s2[j-i] != s1[j] ) {
                done = 1;
                break;
            }
        }
        if (done == 0) {
             cout << s1;
            for (t = k - i + 1; t <= k; t++)
                cout << s2[t];

            cout << endl;
            break;
         }
         done = 0;
    }
    delete s2;

    return 0;
}

For test 'aba' right answer is 'ababa'
Read the problem more attentively. String should be not empty!

Good luck!

Thanks, now all right, next time I'll be more attentive