>>476
#include <stdio.h>
#include <stdlib.h>
int main(void)
{
int n,a=1,d=1,sum;
char buf[256]={"\0"};
size_t buf_sz=sizeof(buf)/sizeof(buf[0]),i;
printf("整数nの入力==>");
fgets(buf,buf_sz,stdin);
n=atoi(buf);
sum= (n*(2*a+(n-1)*d)) / 2;
printf("童貞:%d",sum);
return 0;
}