#include<stdio.h>
#include<stdlib.h>
int main(void){
	int  N,n,sum;
	printf("请输入孩子数量\n");
	scanf("%d",&N);
	if(1<=N<=100){	sum=0;
	for(n=1;n<=N;n=n+1){
     sum=sum+n;
	}
    printf("Sum is %d.\n",sum);
    return 0;
	}

}