What is the output of the following program?

#include<stdio.h>
int main() {
    int i = 0, j = 0;
    char str[10] = "abcdef";
    char str2[10];
    while (str[i] != '\0') {
        i++;
    }
    str2[i] = '\0';
    while (i >= 0) {
        str2[--i] = str[j++];
    }
    printf("%s\n", str2);
    return 0;
}