// verifast_options{disable_overflow_check target:ILP32}
extern void abort(void);
//@ requires true;
//@ ensures true;
void reach_error()
//@ requires false;
//@ ensures true;
{}
/*
 * 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, true);
//@ ensures junk();
{
    //@ open_module(); 
    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();}
    }
 return 0; }