1.
#include <iostream>
using namespace std;
int main()
{
unsigned n, i, s=0;
cin>>n;
for(i=0; i<n; i++)
s=s+i;
cout<<s;
return 0;
}
2.
#include <iostream>
using namespace std;
int main()
{
unsigned n, i=0, s=0;
cin>>n;
while(n)
{
if(i%2==1)
{
s=s+i;
n--;
}
i++;
}
cout<<s;
return 0;
}
3.
#include <iostream>
using namespace std;
int main()
{
unsigned n, i=0, s=0;
cin>>n;
while(n)
{
if(i%2==0)
{
s=s+i;
n--;
}
i++;
}
cout<<s;
return 0;
}
4.
#include <iostream>
using namespace std;
int main()
{
unsigned n, i=0, s=0;
cin>>n;
for(i=0; i<n; i++)
s=s+i*i;
cout<<s;
return 0;
}