C :

#include<stdio.h>
#include<string.h>
void main()
{
	int n,i=0,sum=0;
	scanf("%d",&n);
	   while(i!=n+1)
	   {
		   sum=sum+2*i;
		   i++;
	   }
   printf("%d",sum);
}

C++ :

#include<stdio.h>
int main()
{int n,sum=0,i;
 scanf("%d",&n);
 for(i=0;i<=2*n;)
  { sum=sum+i;
    i=i+2;
 }
printf("%d",sum);
return 0;
}