#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>#include <cmath>using namespace std;#define eps 1.0e-8double c, l1, n;double cal(double b){ double a = l1 /2; double d = sqrt(a * a + b * b); double h = a * d / b; double r = sqrt(h * h + d * d) /2; return atan(b / (l1 /2)) *4* r;}int main(){ while (scanf("%lf%lf%lf", &l1, &n, &c) != EOF) { if (n <0&& l1 <0&& c <0) break; double l2 = l1 * (n * c +1); if (l2 - l1 < eps) { printf("0.000n"); continue; } double l = eps; double r = l1 /2; double mid; while (abs(l - r) > eps) { mid = (l + r) /2; double x = cal(mid); if (abs(x - l2) < eps) break; if (x > l2) r = mid - eps; else l = mid + eps; } printf("%.3fn", mid); } return 0;}
