#include <bits/stdc++.h>
using namespace std;
const long long inf = (long long)1e18;
const long long mod = (long long)1e9 + 7;
const double eps = (double)1e-9;
const double pi = acos(-1.0);
const int dx[] = {0, 0, 1, 0, -1};
const int dy[] = {0, 1, 0, -1, 0};
const int N = 100500;
long long dp[N], t[N << 2];
int n, m, x[N], s[N];
void build(int v, int l, int r) {
  if (l == r) {
    t[v] = dp[r];
    return;
  }
  int mid = (l + r) >> 1;
  build(v << 1, l, mid);
  build(v << 1 | 1, mid + 1, r);
  t[v] = min(t[v << 1], t[v << 1 | 1]);
}
void upd(int v, int l, int r, int pos) {
  if (l == r) {
    t[v] = dp[pos];
    return;
  }
  int mid = (l + r) >> 1;
  if (pos <= mid)
    upd(v << 1, l, mid, pos);
  else
    upd(v << 1 | 1, mid + 1, r, pos);
  t[v] = min(t[v << 1], t[v << 1 | 1]);
}
long long get(int v, int l, int r, int lx, int rx) {
  if (rx < l || r < lx) return inf;
  if (lx <= l && r <= rx) return t[v];
  int mid = (l + r) >> 1;
  return min(get(v << 1, l, mid, lx, rx), get(v << 1 | 1, mid + 1, r, lx, rx));
}
int main() {
  cin >> n >> m;
  for (int i = 1; i <= n; i++) cin >> x[i] >> s[i];
  for (int i = 1; i <= m; i++) dp[i] = inf;
  build(1, 0, m - 1);
  for (int i = 1; i <= m; i++) {
    dp[i] = dp[i - 1] + 1;
    for (int j = 1; j <= n; j++) {
      int l = x[j] - s[j];
      int r = x[j] + s[j];
      if (i < l) continue;
      int cost = 0;
      if (r < i) {
        cost = i - r;
        r += cost;
        l -= cost;
      }
      if (max(0, l - 1) < i)
        dp[i] = min(dp[i], get(1, 0, m - 1, max(0, l - 1), i - 1) + cost);
    }
    if (i < m) upd(1, 0, m - 1, i);
  }
  cout << dp[m];
  return 0;
}
