Sum Problem(1001)

#include<stdio.h>
int main()
{
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        printf("%.f\n\n",(1+n)/2.0*n);
    }
}

#include<stdio.h>
int main()
{
int i,n;
__int64 sum;
while(scanf("%d",&n)!=EOF)
{
sum=0;
for(i=1;i<=n;i++)
           sum+=i;
printf("%I64d\n\n",sum);
} 
return 0;
}

Original