#include <bits/stdc++.h>
using namespace std;
const long long INF = 1ll << 60;
vector<long long> lucky;
long long cur = 0;
void gen_lucky(int len = 1) {
  if (len > 18)
    return;
  else {
    cur = cur * 10ll + 4ll;
    lucky.push_back(cur);
    gen_lucky(len + 1);
    cur /= 10ll;
    cur = cur * 10ll + 7ll;
    lucky.push_back(cur);
    gen_lucky(len + 1);
    cur /= 10ll;
  }
}
bool comp(const pair<long long, bool> &a, const pair<long long, bool> &b) {
  return a.first < b.first || (a.first == b.first && a.second);
}
vector<pair<long long, long long> > a;
vector<pair<long long, char> > b, bb;
long long lft[528000], rght[528000];
int main() {
  int n;
  long long k, minsize = INF;
  cin >> n >> k;
  a.resize(n);
  for (int i = 0; i < n; ++i)
    cin >> a[i].first >> a[i].second,
        minsize = min(minsize, a[i].second - a[i].first);
  lucky.reserve(528000);
  gen_lucky();
  for (int i = 0; i < lucky.size(); ++i) lft[i] = INF, rght[i] = INF;
  b.reserve(630000);
  bb.reserve(630000);
  sort(lucky.begin(), lucky.end());
  for (int i = 0; i < lucky.size(); ++i) bb.push_back(make_pair(lucky[i], 1));
  b = bb;
  for (int i = 0; i < n; ++i) b.push_back(make_pair(a[i].second, 0));
  sort(b.begin() + lucky.size(), b.end(), comp);
  inplace_merge(b.begin(), b.begin() + lucky.size(), b.end(), comp);
  long long cnt = 0, cost = 0;
  int lcnt = 0;
  if (!b[0].second)
    cnt++;
  else
    lcnt++, lft[0] = 0;
  for (int i = 1; i < b.size(); ++i) {
    cost += cnt * (b[i].first - b[i - 1].first);
    if (cost > k || cost < 0) break;
    if (b[i].second)
      lft[lcnt++] = cost;
    else
      cnt++;
  }
  b = bb;
  for (int i = 0; i < n; ++i) b.push_back(make_pair(a[i].first, 0));
  sort(b.begin() + lucky.size(), b.end(), comp);
  inplace_merge(b.begin(), b.begin() + lucky.size(), b.end(), comp);
  reverse(b.begin(), b.end());
  lcnt = lucky.size() - 1, cnt = 0, cost = 0;
  for (int i = 1; i < b.size(); ++i) {
    cost += cnt * (b[i - 1].first - b[i].first);
    if (cost > k || cost < 0) break;
    if (b[i].second)
      rght[--lcnt] = cost;
    else
      cnt++;
  }
  int r = 0, ans = 0;
  for (int i = 0; i < lucky.size(); ++i) {
    r = max(i, r);
    while (r < lucky.size() && lucky[r] - lucky[i] <= minsize &&
           lft[r] + rght[i] <= k) {
      ans = max(ans, r - i + 1);
      r++;
    }
  }
  cout << ans;
  return 0;
}
