#define EPS 1e-10
#define equals(a, b) (fabs((a) - (b)) < EPS)
#include <cstdio>
#include <cmath>
#include <vector>
#include <algorithm>
#include <utility>
#include <cassert>
using namespace std;
#define INF 0x3f3f3f3f

// definition of turning
static const int COUNTER_CLOCKWISE = 1;
static const int CLOCKWISE = -1;
static const int ONLINE_BACK = 2;
static const int ONLINE_FRONT = -2;
static const int ON_SEGMENT = 0;

class Point
{
public:
  double x, y;
  Point (double x = 0, double y = 0) : x(x), y(y) {}
  Point operator + (Point p) {return Point(x + p.x, y + p.y); }
  Point operator - (Point p) {return Point(x - p.x, y - p.y); }
  Point operator * (double a) {return Point(a * x, a * y); }
  Point operator / (double a) {return Point(x / a, y / a); }

  double norm() { return x * x + y * y; }
  double abs() { return sqrt(norm()); }

  bool operator < (const Point &p) const
  {
    return x != p.x ? x < p.x : y < p.y;
  }

  bool operator == (const Point &p) const
  {
    return equals(x, p.x) && equals(y, p.y);
  }
};

typedef Point Vector;
typedef vector<Point> Polygon;

struct Segment
{
  Point p1, p2;
  Segment() {}
  Segment(Point p1, Point p2) : p1(p1), p2(p2) {}
  Segment(double x1, double y1, double x2, double y2)
  {
    p1 = Point(x1, y1);
    p2 = Point(x2, y2);
  }
};

typedef Segment Line;

class Circle
{
public:
  Point c;
  double r;
  Circle(Point c = Point(), double r = 0.0) : c(c), r(r) {}
};


// dot and cross product
double dot(Vector a, Vector b)
{
  return a.x * b.x + a.y * b.y;
}

double cross(Vector a, Vector b)
{
  return a.x * b.y - a.y * b.x;
}

// orthogonality
bool isOrthagonal(Vector a, Vector b)
{
  return equals(dot(a, b), 0.0);
}

bool isOrthagonal(Point a1, Point a2, Point b1, Point b2)
{
  return isOrthagonal(a1 - a2, b1 - b2);
}

bool isOrthagonal(Segment s1, Segment s2)
{
  return isOrthagonal(s1.p1 - s1.p2, s2.p1 - s2.p2);
}

// parallelism
bool isParallel(Vector a, Vector b)
{
  return equals(cross(a, b), 0.0);
}

bool isParallel(Point a1, Point a2, Point b1, Point b2)
{
  return isParallel(a1 - a2, b1 - b2);
}

bool isParallel(Segment s1, Segment s2)
{
  return isParallel(s1.p1 - s1.p2, s2.p1 - s2.p2);
}

// projection & reflection
Point project(Segment s, Point p)
{
  Vector base = s.p2 - s.p1;
  double r = dot(p - s.p1, base) / base.norm();
  return s.p1 + base * r;
}

Point reflect(Segment s, Point p)
{
  return p + (project(s, p) - p) * 2.0;
}

// distance
double getDistance(Point a, Point b)
{
  return (a - b).abs();
}

double getDistanceLP(Line l, Point p)
{
  return abs(cross(l.p1 - l.p2, p - l.p1)) / (l.p2 - l.p1).abs();
}

double getDistanceSP(Segment s, Point p)
{
  if (dot(p - s.p1, s.p2 - s.p1) < 0) return getDistance(p, s.p1);
  if (dot(p - s.p2, s.p1 - s.p2) < 0) return getDistance(p, s.p2);
  return getDistanceLP(s, p);
}

bool intersect(Point p1, Point p2, Point p3, Point p4);
bool intersect(Segment s1, Segment s2);
double getDistanceSS(Segment s1, Segment s2)
{
  if (intersect(s1, s2)) return 0.0;
  return min(min(getDistanceSP(s1, s2.p1), getDistanceSP(s1, s2.p2)), \
            min(getDistanceSP(s2, s1.p1), getDistanceSP(s2, s1.p2)));
}

//ccw
int ccw(Point p0, Point p1, Point p2)
{
  Vector a = p1 - p0;
  Vector b = p2 - p0;
  if (cross(a, b) > EPS) return COUNTER_CLOCKWISE;
  if (cross(a, b) < -EPS) return CLOCKWISE;
  if (dot(a, b) < -EPS) return ONLINE_BACK;
  if (a.norm() < b.norm()) return ONLINE_FRONT;
  return ON_SEGMENT;
}

// intersection
bool intersect(Point p1, Point p2, Point p3, Point p4)
{
  return (ccw(p1, p2, p3) * ccw(p1, p2, p4) <= 0 && \
          ccw(p3, p4, p1) * ccw(p3, p4, p2) <= 0);
}

bool intersect(Segment s1, Segment s2)
{
  return intersect(s1.p1, s1.p2, s2.p1, s2.p2);
}

// Cross point
Point getCrossPoint(Segment s1, Segment s2)
{
  Vector base = s2.p2 - s2.p1;
  double d1 = abs(cross(base, s1.p1 - s2.p1));
  double d2 = abs(cross(base, s1.p2 - s2.p1));
  double t = d1 / (d1 + d2);
  return s1.p1 + (s1.p2 - s1.p1) * t;
}

// Cross points of a circle and a line
pair<Point, Point> getCrossPoints(Circle c, Line l)
{
  Vector pr = project(l, c.c);
  Vector e = (l.p2 - l.p1) / (l.p2 - l.p1).abs();
  double base = sqrt(c.r * c.r - (pr - c.c).norm());
  return make_pair(pr + e * base, pr - e * base);
}

// Cross points of two circles
double arg(Vector p) { return atan2(p.y, p.x); }
Vector polar(double a, double r) { return Point(cos(r) * a, sin(r) * a); }
pair<Point, Point> getCrossPoints(Circle c1, Circle c2)
{
  double d = (c1.c - c2.c).abs();
  double a = acos((c1.r * c1.r + d * d - c2.r * c2.r) / (2 * c1.r * d));
  double t = arg(c2.c - c1.c);
  return make_pair(c1.c + polar(c1.r, t + a), c1.c + polar(c1.r, t - a));
}

int contains(Polygon g, Point p)
{
  int n = g.size();
  bool x = false;
  for (int i = 0; i < n; i++)
  {
    Point a = g[i] - p, b = g[(i + 1) % n] - p;
    if (abs(cross(a, b)) < EPS && dot(a, b) < EPS) return 1;
    if (a.y > b.y) swap(a, b);
    if (a.y < EPS && EPS < b.y && cross(a, b) < EPS) x = !x;
  }
  return (x ? 2 : 0);
}

Polygon andrewScan(Polygon s)
{
  Polygon u, l;
  if (s.size() < 3) return s;
  sort(s.begin(), s.end());
  u.push_back(s[0]);
  u.push_back(s[1]);
  l.push_back(s[s.size() - 1]);
  l.push_back(s[s.size() - 2]);

  for (int i = 2; i < s.size(); i++)
  {
    for (int n = u.size(); n >= 2 && ccw(u[n - 2], u[n - 1], s[i]) != CLOCKWISE; n--)
    {
      u.pop_back();
    }
    u.push_back(s[i]);
  }

  for (int i = s.size() - 3; i >= 0; i--)
  {
    for (int n = l.size(); n >= 2 && ccw(l[n - 2], l[n - 1], s[i]) != CLOCKWISE; n--)
    {
      l.pop_back();
    }
    l.push_back(s[i]);
  }
  reverse(l.begin(), l.end());
  for (int i = u.size() - 2; i >= 1; i--) l.push_back(u[i]);
  return l;
}

int main()
{
  #ifdef DEBUG
  freopen("in.txt", "r", stdin);
  #endif
  double d;
  while (~scanf("%lf", &d) && fabs(d) > EPS)
  {
    double px, py, vx, vy;
    double travel;
    scanf("%lf%lf%lf%lf", &px, &py, &vx, &vy);
    Vector v1 = Vector(px, py), v2 = Vector(vx, vy);
    double jj = dot(v1, v2) / (v1.abs() * v2.abs());
    if (fabs(jj + 1.0) < EPS) travel = v1.abs();
    else if (fabs(jj - 1.0) < EPS) travel = 2.0 - v1.abs();
    else travel = INF;
    if (d - travel >= EPS) printf("%.10lf\n", travel);
    else printf("impossible\n");
  }
}



Measured memory_bytes: 2640