// verifast_options{disable_overflow_check target:ILP32}

extern void abort(void);//@ requires true; 
//@ ensures true;

extern void __assert_fail(const char *, const char *, unsigned int, const char *) __attribute__ ((__nothrow__ , __leaf__)) __attribute__ ((__noreturn__));
void reach_error() //@ requires false; 
//@ ensures true;
{ __assert_fail("0", "recHanoi03-2.c", 3, "reach_error"); }

/*
 * recHanoi.c
 *
 *  Created on: 17.07.2013
 *      Author: Stefan Wissert
 */

extern int __VERIFIER_nondet_int(void);//@ requires true; 
//@ ensures true;


/*
 * This function returns the optimal amount of steps,
 * needed to solve the problem for n-disks
 */
int hanoi(int n) //@ requires true; 
//@ ensures (((((((3 <= result) && (n <= 2)) || (126 < result)) || (((n + 11) <= result) && (31 <= result))) || ((result == 1) && (n == 1))) || ((7 <= result) && (n <= 3))) || ((15 <= result) && (n <= 4)));
{
    if (n == 1) {
		return 1;
	}
	return 2 * (hanoi(n-1)) + 1;
}


int main() //@ requires module(recHanoi03_2__verifast_instrumented_modified, true); 
//@ ensures junk();
{
    int n = __VERIFIER_nondet_int();
    if (n < 1 || n > 31) {
    	return 0;
    }
    int result = hanoi(n);
    if (result >= n) {
        return 0;
    } else {
        ERROR: {reach_error();abort();}
    }
}