import java.awt.geom.Line2D; import java.io.ByteArrayInputStream; import java.io.IOException; import java.io.InputStream; import java.io.PrintWriter; import java.util.Arrays; import java.util.Comparator; import java.util.InputMismatchException; public class Main { static InputStream is; static PrintWriter out; static String INPUT = ""; static void solve() { int n = ni(); if(n == 0){ out.println(1); return; } int[][] co = new int[n][]; long[] codes = new long[n]; for(int i = 0;i < n;i++){ co[i] = new int[]{ni(), ni()}; codes[i] = co[i][0]+20000L<<48|co[i][1]+20000L<<32|i+1; } Arrays.sort(codes); int p = 0; for(int i = 0;i < n;i++){ if(i == 0 || codes[i]>>>32 != codes[i-1]>>>32){ codes[p++] = codes[i]; } } codes = Arrays.copyOf(codes, p); DJSet ds = new DJSet(n); for(int i = 0;i < n;i++){ int x = co[i][0], y = co[i][1]; for(int j = -10;j <= 10;j++){ for(int k = -10;k <= 10;k++){ if(j*j+k*k <= 100){ int dx = x + j, dy = y + k; long low = (long)dx+20000L<<48|dy+20000L<<32|0; int ind = Arrays.binarySearch(codes, low); ind = -ind-1; if(ind < codes.length && codes[ind]>>>32 == low>>>32){ ds.union(((int)codes[ind])-1, i); } } } } } int[][] g = makeBuckets(ds); double max = 0; for(int[] row : g){ int m = row.length; double[][] lco = new double[m][]; for(int i = 0;i < m;i++){ lco[i] = new double[]{co[row[i]][0], co[row[i]][1]}; } double[][] hull = convexHull(lco); max = Math.max(max, findMostFarPair(hull) + 2); } out.printf("%.12f\n", max); } public static double findMostFarPair(double[][] co) { int h = co.length; if(h <= 1)return 0.; int is = 0, js = 0; for(int j = 1;j < h;j++){ if(co[j][1] > co[is][1])is = j; if(co[j][1] < co[js][1])js = j; } double max = (co[is][0]-co[js][0])*(co[is][0]-co[js][0])+ (co[is][1]-co[js][1])*(co[is][1]-co[js][1]); int i, maxi, j, maxj; i = maxi = is; j = maxj = js; int ii = i+1, jj = j+1; if(ii >= h)ii -= h; if(jj >= h)jj -= h; do{ double ax = co[ii][0]-co[i][0]; double ay = co[ii][1]-co[i][1]; double bx = co[jj][0]-co[j][0]; double by = co[jj][1]-co[j][1]; if(ax*by-ay*bx >= 0){ j = jj; jj = j+1; if(jj >= h)jj -= h; }else{ i = ii; ii = i+1; if(ii >= h)ii -= h; } double nor = (co[i][0]-co[j][0])*(co[i][0]-co[j][0])+ (co[i][1]-co[j][1])*(co[i][1]-co[j][1]); if(nor > max){ max = nor; maxi = i; maxj = j; } }while(i != is || j != js); return Math.sqrt(max); } public static double[][] convexHull(double[][] co) { int n = co.length; if(n <= 1)return co; Arrays.sort(co, new Comparator(){ public int compare(double[] a, double[] b){ if(a[0] - b[0] != 0)return (int)Math.signum(a[0] - b[0]); return (int)Math.signum(a[1] - b[1]); } }); int[] inds = new int[n + 1]; int p = 0; for(int i = 0;i < n;i++){ if(p >= 1 && co[inds[p-1]][0] == co[i][0] && co[inds[p-1]][1] == co[i][1])continue; while(p >= 2 && Line2D.relativeCCW( co[inds[p-2]][0], co[inds[p-2]][1], co[inds[p-1]][0], co[inds[p-1]][1], co[i][0], co[i][1]) == 1)p--; inds[p++] = i; } int inf = p + 1; for(int i = n - 2;i >= 0;i--){ if(co[inds[p-1]][0] == co[i][0] && co[inds[p-1]][1] == co[i][1])continue; while(p >= inf && Line2D.relativeCCW( co[inds[p-2]][0], co[inds[p-2]][1], co[inds[p-1]][0], co[inds[p-1]][1], co[i][0], co[i][1]) == 1)p--; inds[p++] = i; } double[][] ret = new double[p-1][]; for(int i = 0;i < p-1;i++)ret[i] = co[inds[i]]; return ret; } public static int[][] makeBuckets(DJSet ds) { int n = ds.upper.length; int[] roots = new int[n]; int[] where = new int[n]; int p = 0; for(int i = 0;i < n;i++){ if(ds.upper[i] < 0){ roots[p++] = i; where[i] = p-1; } } int[][] bucket = new int[p][]; for(int i = 0;i < p;i++){ bucket[i] = new int[-ds.upper[roots[i]]]; } int[] bp = new int[p]; for(int i = 0;i < n;i++){ int ind = where[ds.root(i)]; bucket[ind][bp[ind]++] = i; } return bucket; } public static class DJSet { public int[] upper; public DJSet(int n) { upper = new int[n]; Arrays.fill(upper, -1); } public int root(int x) { return upper[x] < 0 ? x : (upper[x] = root(upper[x])); } public boolean equiv(int x, int y) { return root(x) == root(y); } public boolean union(int x, int y) { x = root(x); y = root(y); if (x != y) { if (upper[y] < upper[x]) { int d = x; x = y; y = d; } upper[x] += upper[y]; upper[y] = x; } return x == y; } public int count() { int ct = 0; for (int u : upper) if (u < 0) ct++; return ct; } } public static void main(String[] args) throws Exception { // int n = 120000, m = 99999; // Random gen = new Random(); // StringBuilder sb = new StringBuilder(); // sb.append(n + " "); // for (int i = 0; i < n; i++) { // sb.append(gen.nextInt(20000)-10000 + " "); // sb.append(gen.nextInt(20000)-10000 + " "); // } // INPUT = sb.toString(); long S = System.currentTimeMillis(); is = INPUT.isEmpty() ? System.in : new ByteArrayInputStream(INPUT.getBytes()); out = new PrintWriter(System.out); solve(); out.flush(); long G = System.currentTimeMillis(); tr(G-S+"ms"); } private static boolean eof() { if(lenbuf == -1)return true; int lptr = ptrbuf; while(lptr < lenbuf)if(!isSpaceChar(inbuf[lptr++]))return false; try { is.mark(1000); while(true){ int b = is.read(); if(b == -1){ is.reset(); return true; }else if(!isSpaceChar(b)){ is.reset(); return false; } } } catch (IOException e) { return true; } } private static byte[] inbuf = new byte[1024]; static int lenbuf = 0, ptrbuf = 0; private static int readByte() { if(lenbuf == -1)throw new InputMismatchException(); if(ptrbuf >= lenbuf){ ptrbuf = 0; try { lenbuf = is.read(inbuf); } catch (IOException e) { throw new InputMismatchException(); } if(lenbuf <= 0)return -1; } return inbuf[ptrbuf++]; } private static boolean isSpaceChar(int c) { return !(c >= 33 && c <= 126); } private static int skip() { int b; while((b = readByte()) != -1 && isSpaceChar(b)); return b; } private static double nd() { return Double.parseDouble(ns()); } private static char nc() { return (char)skip(); } private static String ns() { int b = skip(); StringBuilder sb = new StringBuilder(); while(!(isSpaceChar(b))){ // when nextLine, (isSpaceChar(b) && b != ' ') sb.appendCodePoint(b); b = readByte(); } return sb.toString(); } private static char[] ns(int n) { char[] buf = new char[n]; int b = skip(), p = 0; while(p < n && !(isSpaceChar(b))){ buf[p++] = (char)b; b = readByte(); } return n == p ? buf : Arrays.copyOf(buf, p); } private static char[][] nm(int n, int m) { char[][] map = new char[n][]; for(int i = 0;i < n;i++)map[i] = ns(m); return map; } private static int[] na(int n) { int[] a = new int[n]; for(int i = 0;i < n;i++)a[i] = ni(); return a; } private static int ni() { int num = 0, b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private static long nl() { long num = 0; int b; boolean minus = false; while((b = readByte()) != -1 && !((b >= '0' && b <= '9') || b == '-')); if(b == '-'){ minus = true; b = readByte(); } while(true){ if(b >= '0' && b <= '9'){ num = num * 10 + (b - '0'); }else{ return minus ? -num : num; } b = readByte(); } } private static void tr(Object... o) { if(INPUT.length() != 0)System.out.println(Arrays.deepToString(o)); } }