#include <stdio.h>
#include <math.h>
int main()
{
const double r = 2;
const double r2 = r * r;
double x = 0, y = r;
double s = 0;
double n = 100;
double dx;
printf("分割数 : ");
scanf("%d", &n);
dx = r / n;
for (x = 0; x < r; x += dx) {
y = sqrt(r2 - pow(x, 2.0));
s += dx * y;
}
printf("面積 = %f\n", s);
return 0;
}