This problem doesn't need to be as big as long long, and int can pass it.

# include & ltstdio.h & gt

intmain()

{

inti，n，sum

while(scanf("%d "，& ampn)！ =EOF)

{

sum = 0；

for(I = 1； I < = n; i++)

sum = sum+I；

printf("%d\n\n "，sum)；

}

return0

}