All codes listed below works good on my computer (and they give correct answers), but when submitting I get:

Code #1:
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#include<stdio.h>
#include<iostream.h>

int main()
{
  long long n;
  cin>>n;

  long long wynik;
  wynik=(n*(n+1)*(n+2))/2;

  cout<<wynik<<endl;
  return 0;
}
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Compilation error

Code #2: removed iostream.h and replaced cin and cout with
scanf("%lld",%n); and printf("%lld\n",wynik);

WA on test 5

Code #3: same as #2, but with
printf("%0.lf\n, (double)wynik); instead

WA on test 1
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All those programs work and give correct results on my computer. What's wrong here? Please help.

For The First Code :
Add using namespace std; for using cin & cout.