void abort() { };

                                                                       
                                                  
                                                                             
                                                                   
                                                  
                                                                             
                                                                              
                                                                             

                                                                                                                                                                

                                        
/*@ 
    requires ((\old(cond) != 0)) && (cond != 0);
    ensures ((\old(cond) != 0)) && (1);
@*/
void __VERIFIER_assert(int cond) {
  if (!(cond)) {
    ERROR: {/*@ assert(0); */;abort();}
  }
  return;
}
extern int __VERIFIER_nondet_int();
int main() {
  int i, n=__VERIFIER_nondet_int(), sn=0;
  if (!(n < 1000 && n >= -1000)) return 0;
/*@
loop invariant ((((sn == 0) && (i == 1)) || ((sn <= ((long long) n * 2)) && (((long long) 2 + sn) == ((long long) i * 2)))));
@*/
  for(i=1; i<=n; i++) {
    sn = sn + (2);
  }
  __VERIFIER_assert(sn==n*(2) || sn == 0);
}