#include <bits/stdc++.h>
using namespace std;
mt19937 gene(233);
inline char GET_CHAR() {
  const int maxn = 131072;
  static char buf[maxn], *p1 = buf, *p2 = buf;
  return p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, maxn, stdin), p1 == p2)
             ? EOF
             : *p1++;
}
inline int getInt() {
  int res(0);
  char c = getchar();
  while (c < '0') c = getchar();
  while (c >= '0') {
    res = res * 10 + (c - '0');
    c = getchar();
  }
  return res;
}
inline long long fastpo(long long x, long long n, long long mod) {
  long long res(1);
  while (n) {
    if (n & 1) {
      res = res * (long long)x % mod;
    }
    x = x * (long long)x % mod;
    n /= 2;
  }
  return res;
}
inline string itoa(int x, int width = 0) {
  string res;
  if (x == 0) res.push_back('0');
  while (x) {
    res.push_back('0' + x % 10);
    x /= 10;
  }
  while ((int)res.size() < width) res.push_back('0');
  reverse(res.begin(), res.end());
  return res;
}
template <const long long mod>
struct MI {
  long long a;
  MI operator+(const MI& b) {
    MI res{a + b.a};
    if (res.a >= mod) res.a -= mod;
    return res;
  }
  MI operator-(const MI& b) {
    MI res{a - b.a};
    if (res.a <= 0) res.a += mod;
    return res;
  }
  MI operator*(const MI& b) { return MI{a * b.a % mod}; }
  MI operator/(const MI& b) { return MI{a * fastpo(b.a, mod - 2, mod) % mod}; }
};
const int N = 2048599;
const int LOG = 20;
const int mod = 1e9 + 7;
const int inf = 1e9 + 7;
int n, m;
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
vector<int> ans;
vector<pair<int, int>> e[N];
int a[N], b[N], rela[N], deg[N], siz[N], vst[N];
int getr(int x) {
  int p;
  for (p = x; p != rela[p]; p = rela[p])
    ;
  int p1 = p;
  p = x;
  while (p != rela[p]) {
    int p2 = rela[p];
    rela[p] = p1;
    p = p2;
  }
  return p1;
}
int cur[N];
void dfs(int v) {
  for (; cur[v] < (int)e[v].size(); cur[v]++) {
    int y = e[v][cur[v]].first, i = e[v][cur[v]].second;
    if (vst[(i + 1) / 2]) continue;
    vst[(i + 1) / 2] = true;
    dfs(y);
    ans.push_back(i);
    ans.push_back(i % 2 == 0 ? i - 1 : i + 1);
  }
}
int main() {
  int n;
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", &a[i], &b[i]);
  }
  for (int i = 20; i >= 0; i--) {
    if (i == 0) {
      printf("0\n");
      for (int i = 1; i <= n * 2; i++)
        printf("%d%c", i, i == n * 2 ? '\n' : ' ');
      return 0;
    }
    int msk = (1 << i) - 1;
    for (int j = 0; j <= msk; j++) {
      rela[j] = j;
      siz[j] = 0;
      deg[j] = 0;
    }
    for (int j = 1; j <= n; j++) {
      deg[a[j] & msk]++;
      deg[b[j] & msk]++;
      int x = getr(a[j] & msk), y = getr(b[j] & msk);
      if (x != y) {
        rela[x] = y;
        siz[y] += siz[x];
      }
      siz[y]++;
    }
    bool flag = true;
    int cnt = 0, bg = 0;
    for (int j = 0; j < (1 << i); j++) {
      if (deg[j] % 2 == 1) {
        flag = false;
      }
      if (rela[j] == j && siz[j] != 0) {
        cnt++;
        bg = j;
      }
    }
    if (flag && cnt == 1) {
      for (int j = 1; j <= n; j++) {
        e[a[j] & msk].push_back(make_pair(b[j] & msk, j * 2));
        e[b[j] & msk].push_back(make_pair(a[j] & msk, j * 2 - 1));
      }
      dfs(bg);
      printf("%d\n", i);
      for (int i = 0; i < 2 * n; i++)
        printf("%d%c", ans[i], i == n * 2 - 1 ? '\n' : ' ');
      return 0;
    }
  }
}
