>>3
% gcc --version
gcc (GCC) 4.1.2 20080704 (Red Hat 4.1.2-50)
% uname -a
Linux (ホスト名) 2.6.18-238.12.1.el5 #1 SMP Tue May 31 13:22:04 EDT 2011 x86_64 x86_64 x86_64 GNU/Linux
% cat ack.c
#include <stdio.h>

int ack(int m, int n)
{
if (m == 0) return n+1;
if (n == 0) return ack(m-1, 1);
return ack(m-1, ack(m, n-1));
}

int main()
{
printf("%d\n", ack(4, 1));
return 0;
}
% gcc ack.c
% time ./a.out
65533
./a.out 24.65s user 0.79s system 106% cpu 23.969 total