Unable to understand a format string exploitation code

I came across this code showing format string exploitation while reading [this][1] article. #include int main(void) { char secret[]="hack.se is lame"; char buffer[512]; char target[512]; printf("secret = %pn",&secret); fgets(buffer,512,stdin); snprintf(target,512,buffer); printf("%s",target); } Executing it with following input [root@knark]$ ./a.out secret = 0xbffffc68 AAAA%x %x %x %x %x %x %x //Input given AAAA4013fe20 0 0 0 41414141 33313034 30326566 - [root@knark]$ What I understand till now is the sequence of `%x`'s will keep on printing the values at addresses above current `%esp` (I'm assuming that stack is growing downwards towards lower address). What I'm unable to understand is the input given is stored in `buffer` array which can't be less than 512 bytes away from current `%esp`. So, how can the output contain `41414141` (the hex representation of `AAAA`) just after the 4 `%x`, i.e, just above the 4 addresses of current `%esp`. I tried hard to stare at assembly code too but I think I couldn't follow the manipulation of strings on stack. [1]: http://www.loko.nu/formatstring/format_string.htm

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