//递归计算自然数前N项的和
#include <stdio.h>
#include <stdlib.h>
long sum(int n){//每个long型占4个字节,数的范围比int大
if(n==0){return 0;}
else if(n==1){return 1;}
else {return n+sum(n-1);}
}
int main(){
int n,s;
scanf("%d",&n);
s=sum(n);
printf("%d\n",s);
system("pause");
return 0;
}