#include <stdio.h>
#include <string.h>
void func(char *b)
{
    char *a= b + 1;
    printf("input  = %s\n", b);
    while (*a)
    {
        if (strlen(a) == (int)(a - b) && strncmp(a, b, strlen(a)) == 0)
        {
            printf("repeat = %.*s\n\n", (int)(a - b), b);
            return;
        }
        ++a;
    }
    printf("repeat unit not found!\n");
    return;
}
int main()
{
    func("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa");
    func("123412312341231234123123412312341231234123");
    func("oxoxoxoxoxoxoxoxxoxoxoxoxoxoxoxoxx");
    func("axaxa");
    return 0;
}