#include <iostream>
using namespace std;
int main()
{
int i, n, sum = 0;
// read n from the user
cin >> n;
// sum up all numbers <=n that are divisible by 3
for (i = 1; i <= n; i++)
if (i%3 == 0)
sum = sum + i;
// print out the sum
cout << "sum is " << sum << endl;
return 0;
}
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