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#include <stdio.h>
int main()
{
int n;
while(scanf("%d",&n)!=EOF)
{
if(n%2==0)
printf("%d\n\n",n/2*(n+1));
else
printf("%d\n\n",(n+1)/2*n);
}
}
#include <stdio.h>
int main()
{
int n;
while(scanf("%d",&n)!=EOF)
printf("%d\n\n",(long long)n*(n+1)/2);
}