#include <bits/stdc++.h>
using namespace std;
const double eps = 1e-9;
const int inf = 2000000000;
const long long infLL = 9000000000000000000;
template <typename first, typename second>
ostream& operator<<(ostream& os, const pair<first, second>& p) {
  return os << "(" << p.first << ", " << p.second << ")";
}
template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v) {
  os << "{";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "}";
}
template <typename T>
ostream& operator<<(ostream& os, const set<T>& v) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin()) os << ",";
    os << *it;
  }
  return os << "]";
}
template <typename T>
ostream& operator<<(ostream& os, const multiset<T>& v) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin()) os << ", ";
    os << *it;
  }
  return os << "]";
}
template <typename first, typename second>
ostream& operator<<(ostream& os, const map<first, second>& v) {
  os << "[";
  for (auto it = v.begin(); it != v.end(); ++it) {
    if (it != v.begin()) os << ", ";
    os << it->first << " = " << it->second;
  }
  return os << "]";
}
void faltu() { cerr << '\n'; }
template <typename T>
void faltu(T a[], int n) {
  for (int i = 0; i < n; ++i) cerr << a[i] << ' ';
  cerr << '\n';
}
template <typename T, typename... hello>
void faltu(T arg, const hello&... rest) {
  cerr << arg << ' ';
  faltu(rest...);
}
const int mx = 1e5 + 5;
int n, m;
int dp[mx];
pair<int, int> p[85];
int main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  ;
  cin >> n >> m;
  for (int i = 0; i < n; ++i) {
    int x, s;
    cin >> x >> s;
    p[i] = make_pair(x, s);
  }
  for (int i = 0; i <= m + 2; ++i) dp[i] = i;
  for (int i = 1; i <= m; ++i) {
    for (int j = 0; j < n; ++j) {
      int x = p[j].first, s = p[j].second;
      int L = max(x - s, 1), R = min(x + s, m);
      if (i >= L && i <= R) {
        dp[i] = min(dp[i - 1], dp[i]);
        break;
      } else if (i < L) {
        dp[i] = min(dp[i], dp[i - 1] + L - i);
      } else if (i > R) {
        int u = max(1, x - (i - x));
        dp[i] = min(dp[i], i - R + dp[u - 1]);
      }
    }
  }
  cout << dp[m] << '\n';
}
