void abort() { };
                                                                                                                                                          
                                                                             

/*
 * Implementation the Ackermann function.
 * http://en.wikipedia.org/wiki/Ackermann_function
 * 
 * Author: Matthias Heizmann
 * Date: 2013-07-13
 * 
 */

extern int __VERIFIER_nondet_int();

/*@ 
    requires (1);
    ensures ((((n < \result) || (m != 0)) && ((0 < m) || (m == 0))));
@*/
int ackermann(int m, int n) {
    if (m==0) {
        return n+1;
    }
    if (n==0) {
        return ackermann(m-1,1);
    }
    return ackermann(m-1,ackermann(m,n-1));
}


int main() {
    int m = __VERIFIER_nondet_int();
    if (m < 0 || m > 3) {
        // additional branch to avoid undefined behavior 
        // (because of signed integer overflow)
        return 0;
    }
    int n = __VERIFIER_nondet_int();
    if (n < 0 || n > 23) {
        // additional branch to avoid undefined behavior 
        // (because of signed integer overflow)
        // 
        return 0;
    }
    int result = ackermann(m,n);
    if (m < 2 || n < 2 || result >= 7) {
        return 0;
    } else {
        ERROR: {/*@ assert(0); */;abort();}
    }
}