#include <bits/stdc++.h>
using namespace std;
const int MAXL = 19;
const int MAXN = 100010;
const int MAXM = (1 << MAXL);
int n;
long long k;
long long inv_len;
vector<long long> lucknum;
long long lsum[MAXM], rsum[MAXM];
long long L[MAXN], R[MAXN];
void init() {
  scanf("%d%lld", &n, &k);
  inv_len = (1ll << 62);
  long long l, r;
  for (int i = 0; i < n; ++i) {
    scanf("%lld%lld", &l, &r);
    inv_len = min(inv_len, r - l);
    R[i] = r;
    L[i] = l;
  }
}
void lucknum_cal() {
  lucknum.clear();
  for (int len = 1; len < MAXL; ++len)
    for (int limit = (1 << len), num = 0; num < limit; ++num) {
      long long cur = 0;
      for (int l = len - 1; l >= 0; --l)
        cur = cur * 10 + ((num & (1 << l)) ? 7 : 4);
      lucknum.push_back(cur);
    }
}
void solve() {
  lucknum_cal();
  sort(L, L + n);
  sort(R, R + n);
  long long cur_sum = 0;
  int pt = 0;
  for (int i = 0; i < lucknum.size(); ++i) {
    for (; pt < n && R[pt] < lucknum[i]; ++pt) cur_sum += R[pt];
    if (i > 0 && rsum[i - 1] > k)
      rsum[i] = k + 1;
    else {
      rsum[i] = lucknum[i] * pt - cur_sum;
      if (rsum[i] > k) rsum[i] = k + 1;
    }
  }
  cur_sum = 0;
  pt = n - 1;
  for (int i = lucknum.size() - 1; i >= 0; --i) {
    for (; pt >= 0 && L[pt] > lucknum[i]; --pt) cur_sum += L[pt];
    if (i < lucknum.size() && lsum[i + 1] > k)
      lsum[i] = k + 1;
    else {
      lsum[i] = cur_sum - lucknum[i] * (n - 1 - pt);
      if (lsum[i] > k) lsum[i] = k + 1;
    }
  }
  int ans = 0, lf = 0;
  long long remain;
  for (int head = 0, tail = 0; tail < lucknum.size(); ++tail) {
    for (; lucknum[tail] - lucknum[head] > inv_len; ++head)
      ;
    remain = k - rsum[tail];
    for (; lf < lucknum.size() && lsum[lf] > remain; ++lf)
      ;
    ans = max(ans, tail - max(head, lf) + 1);
  }
  printf("%d\n", ans);
}
int main() {
  init();
  solve();
  return 0;
}
