//用do-while算1到n的和
int main()
{
int n;
int sum=0;
int i=0;
scanf("%d",&n);
do{
i++;
sum+=i;
}while(i<n);
printf("%d\n",sum);
return 0;
}//用do-while算1到n的和
int main()
{
int n;
int sum//用do-while算1到n的和
int main()
{
int n;
int sum=0;
int i=0;
scanf("%d",&n);
do{
i++;
sum+=i;
}while(i<n);
printf("%d\n",sum);
return 0;
}//用do-while算1到n的和
int main()
{
int n;
int sum