Complex recursion problem in C++ Ackermann function

The Ackermann function is a computable function which grows very, very quickly as its inputs grow. For example, while   and  are equal to  and  respectively, .

The Ackermann function can be defined as follows:

What are the last 3 digits of  

#include<iostream>

using namespace std;

int ack(long int m, long int n);

int main()

{

long int m, n,a ;

cout << "enter the m and n  : ";

cin >> m>>n;

a = ack(m, n);

cout << "Ackermann function (" << m << "," << n << ")" << "=" << a <<endl;

return 0;

}

int ack(long int m, long int n)

{

if (m==0) return (n+1);

if (m > 0 && n == 0) return (ack(m - 1, 1));

if (m > 0 && n > 0) return (ack(m - 1, ack(m, n - 1)));

}

output:

enter the m and n  : 3 9
Ackermann function (3,9)=4093

Process returned 0 (0x0)   execution time : 6.553 s

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