#include <bits/stdc++.h>
using namespace std;
int n;
long long k;
long long l[100000], r[100000];
long long dl[100000], dr[100000];
vector<long long> v;
long long maxp = 1000LL * 1000 * 1000 * 1000 * 1000 * 1000;
void get(int i, int l, long long a) {
  if (i == l) {
    v.push_back(a);
    return;
  }
  get(i + 1, l, a * 10LL + 4LL);
  get(i + 1, l, a * 10LL + 7LL);
}
bool ans(int ll, int rr) {
  if (v[rr] - v[ll] + 1 > maxp) {
    return false;
  }
  long long sum = 0;
  if (upper_bound(l, l + n, v[ll]) != l + n) {
    int f = distance(l, upper_bound(l, l + n, v[ll]));
    if (3000LL * 1000 * 1000 * 1000 * 1000 * 1000 / v[ll] < n - f) {
      return 0;
    }
    sum += dl[n - 1] - (f > 0 ? dl[f - 1] : 0LL) - v[ll] * 1LL * (n - f);
  }
  if (lower_bound(r, r + n, v[rr]) != r) {
    int f = distance(r, lower_bound(r, r + n, v[rr])) - 1;
    if (3000LL * 1000 * 1000 * 1000 * 1000 * 1000 / v[rr] < 1LL * (f + 1)) {
      return 0;
    }
    sum += v[rr] * (f + 1) - dr[f];
  }
  return sum <= k;
}
int main() {
  cin >> n >> k;
  for (int i = 0; i < n; i++) {
    scanf("%I64d %I64d", &l[i], &r[i]);
    maxp = min(maxp, r[i] - l[i] + 1LL);
  }
  sort(l, l + n);
  sort(r, r + n);
  for (int i = 0; i < n; i++) {
    dl[i] = (i > 0 ? dl[i - 1] : 0);
    dl[i] += l[i];
    dl[i] = min(dl[i], 2000LL * 1000 * 1000 * 1000 * 1000 * 1000 + 1LL);
    dr[i] = (i > 0 ? dr[i - 1] : 0);
    dr[i] += r[i];
    dr[i] = min(dr[i], 2000LL * 1000 * 1000 * 1000 * 1000 * 1000 + 1LL);
  }
  for (int i = 1; i <= 18; i++) {
    get(0, i, 0LL);
  }
  int sum = 0;
  for (int i = 0; i < (int)v.size(); i++) {
    if (!ans(i, i)) {
      continue;
    }
    int ll = i;
    int rr = (int)v.size() - 1;
    while (ll != rr) {
      int m = (ll + rr + 1) / 2;
      if (ans(i, m)) {
        ll = m;
      } else {
        rr = m - 1;
      }
    }
    sum = max(sum, ll - i + 1);
  }
  cout << sum << endl;
  return 0;
}
