#include <stdio.h>
#include <string.h>

int main(int argc, char* argv[])
{
    char string[2001];
    int i=0;
    int length;

    scanf("%s",&string);

    length=strlen(string);

        for (i=0;i<length/2;i++)
        {
            string[length-(i+1)]=string[i];
        }


    printf("%s",string);

    return 0;
}

You don't take into account, that your number can be smaller.