#include <stdio.h>#include <string.h>#include <math.h>#include <algorithm>using namespace std;const double sq3 = sqrt(3.0);const double INF = 0x3f3f3f3f;const int d[7][2] = { {0, 0}, {0, -2}, {0, 2}, {-1, -1}, {-1, 1}, {1, -1}, {1, 1}};struct point {double x, y;};double tx, ty;double dis(double x, double y) {return sqrt(x*x+y*y);}point find(double xi, double yi) {int cx = (int)(xi/tx);int cy = (int)(yi/ty);if (cx&1) {if (cy%2 == 0) cy++;} else {if (cy%2) cx++;}point A;double tmp = INF;for (int i = 0; i < 7; i++) {double a = dis((cx+d[i][0])*tx-xi, (cy+d[i][1])*ty-yi);if (a < tmp) {A.x = (cx+d[i][0])*tx;A.y = (cy+d[i][1])*ty;tmp = a;}}return A;}double solve(point A, point B) {int cx = (int)(fabs(A.x-B.x)/tx+0.5);int cy = (int)(fabs(A.y-B.y)/ty+0.5);return max(cx, cy) * sq3;}int main () {double r, x1, y1, x2, y2;while (scanf("%lf%lf%lf%lf%lf", &r, &x1, &y1, &x2, &y2) == 5 && (r||x1||y1||x2||y2)) {tx = 3*r/2; ty = sq3*r/2;point A = find(x1, y1);point B = find(x2, y2);if (fabs(A.x-B.x) < 1e-9 && fabs(A.y-B.y) < 1e-9) {printf("%.3lfn", dis(x1-x2, y1-y2));} else {double len = dis(A.x-x1, A.y-y1) + dis(B.x-x2, B.y-y2);len = len + solve(A, B)*r;printf("%.3lfn", len);}}return 0;}
