// verifast_options{disable_overflow_check target:ILP32}
extern void abort(void);
//@ requires true;
//@ ensures true;


void reach_error()
//@ requires false;
//@ ensures true;
{}void assume_abort_if_not(int cond) 
//@ requires true;
//@ ensures true;
{  if(!cond) {abort();}
}
void __VERIFIER_assert(int cond) 
//@ requires (1 <= cond);
//@ ensures (1 <= cond);
{  if (!(cond)) {
  ERROR: {reach_error();abort();}
  }
  return;
}
int __VERIFIER_nondet_int();
//@ requires true;
//@ ensures true;
int main() 
//@ requires module(gauss_sum__verifast_instrumented, true);
//@ ensures junk();
{
    //@ open_module(); 
    int n, sum, i;
    n = __VERIFIER_nondet_int();
    if (!(1 <= n && n <= 1000)) return 0;
    sum = 0;
for(i = 1; i <= n; i++)
//@ invariant (((i + (sum * 2)) == (i * i)) && (((n + (n * n)) == (sum * 2)) || (i < (n + 1))));
    {
        sum = sum + i;
    }
    __VERIFIER_assert(2*sum == n*(n+1));
    return 0;
}