#include <bits/stdc++.h>
using namespace std;
const double pi = acos(0.0) * 2.0;
const long double eps = 1e-10;
const int step[8][2] = {{-1, 0}, {0, 1}, {1, 0},  {0, -1},
                        {-1, 1}, {1, 1}, {1, -1}, {-1, -1}};
template <class T>
inline T abs1(T a) {
  return a < 0 ? -a : a;
}
template <typename t, typename t1>
t min1(t a, t1 b) {
  return a < b ? a : b;
}
template <typename t, typename... arg>
t min1(t a, arg... arr) {
  return min1(a, min1(arr...));
}
template <typename t, typename t1>
t max1(t a, t1 b) {
  return a > b ? a : b;
}
template <typename t, typename... arg>
t max1(t a, arg... arr) {
  return max1(a, max1(arr...));
}
inline int jud(double a, double b) {
  if (abs(a) < eps && abs(b) < eps)
    return 0;
  else if (abs1(a - b) / abs1(a) < eps)
    return 0;
  if (a < b) return -1;
  return 1;
}
template <typename t>
inline int jud(t a, t b) {
  if (a < b) return -1;
  if (a == b) return 0;
  return 1;
}
template <typename it, typename t1>
inline int find(t1 val, it a, int na, bool f_small = 1, bool f_lb = 1) {
  if (na == 0) return 0;
  int be = 0, en = na - 1;
  if (*a <= *(a + na - 1)) {
    if (f_lb == 0)
      while (be < en) {
        int mid = (be + en + 1) / 2;
        if (jud(*(a + mid), val) != 1)
          be = mid;
        else
          en = mid - 1;
      }
    else
      while (be < en) {
        int mid = (be + en) / 2;
        if (jud(*(a + mid), val) != -1)
          en = mid;
        else
          be = mid + 1;
      }
    if (f_small && jud(*(a + be), val) == 1) be--;
    if (!f_small && jud(*(a + be), val) == -1) be++;
  } else {
    if (f_lb)
      while (be < en) {
        int mid = (be + en + 1) / 2;
        if (jud(*(a + mid), val) != -1)
          be = mid;
        else
          en = mid - 1;
      }
    else
      while (be < en) {
        int mid = (be + en) / 2;
        if (jud(*(a + mid), val) != 1)
          en = mid;
        else
          be = mid + 1;
      }
    if (!f_small && jud(*(a + be), val) == -1) be--;
    if (f_small && jud(*(a + be), val) == 1) be++;
  }
  return be;
}
template <class T>
inline T lowb(T num) {
  return num & (-num);
}
inline int bitnum(unsigned int nValue) { return __builtin_popcount(nValue); }
inline int bitnum(int nValue) { return __builtin_popcount(nValue); }
inline int bitnum(unsigned long long nValue) {
  return __builtin_popcount(nValue) + __builtin_popcount(nValue >> 32);
}
inline int bitnum(long long nValue) {
  return __builtin_popcount(nValue) + __builtin_popcount(nValue >> 32);
}
inline int bitmaxl(unsigned int a) {
  if (a == 0) return 0;
  return 32 - __builtin_clz(a);
}
inline int bitmaxl(int a) {
  if (a == 0) return 0;
  return 32 - __builtin_clz(a);
}
inline int bitmaxl(unsigned long long a) {
  int temp = a >> 32;
  if (temp) return 32 - __builtin_clz(temp) + 32;
  return bitmaxl(int(a));
}
inline int bitmaxl(long long a) {
  int temp = a >> 32;
  if (temp) return 32 - __builtin_clz(temp) + 32;
  return bitmaxl(int(a));
}
long long pow(long long n, long long m, long long mod = 0) {
  if (m < 0) return 0;
  long long ans = 1;
  long long k = n;
  while (m) {
    if (m & 1) {
      ans *= k;
      if (mod) ans %= mod;
    }
    k *= k;
    if (mod) k %= mod;
    m >>= 1;
  }
  return ans;
}
template <class t1, class t2>
inline void add(t1 &a, t2 b, int mod = -1) {
  if (mod == -1) mod = 1000000007;
  a += b;
  while (a >= mod) a -= mod;
  while (a < 0) a += mod;
}
template <class t>
void output1(t arr) {
  for (int i = 0; i < (int)arr.size(); i++) cerr << arr[i] << ' ';
  cerr << endl;
}
template <class t>
void output2(t arr) {
  for (int i = 0; i < (int)arr.size(); i++) output1(arr[i]);
}
const int maxn = 410;
pair<int, int> arr[maxn];
int trans[maxn], ltrans;
int dp[maxn][maxn];
int n;
int rdp[2][maxn];
pair<int, int> to[maxn];
int yuan[maxn];
vector<int> have[maxn];
int main() {
  ios_base::sync_with_stdio(0);
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%d%d", &arr[i].first, &arr[i].second);
    trans[ltrans++] = arr[i].first;
    trans[ltrans++] = arr[i].second + arr[i].first;
    trans[ltrans++] = arr[i].first - arr[i].second;
  }
  sort(trans, trans + ltrans);
  ltrans = unique(trans, trans + ltrans) - trans;
  sort(arr, arr + n);
  for (int i = 0; i < n; i++) {
    to[i] = make_pair(find(arr[i].first - arr[i].second, trans, ltrans),
                      find(arr[i].first + arr[i].second, trans, ltrans));
    arr[i].first = find(arr[i].first, trans, ltrans);
    have[arr[i].first].push_back(i);
  }
  for (int i = 0; i < ltrans; i++)
    for (int j = 0; j < ltrans; j++) dp[i][j] = -1000000007;
  memset(dp[0], 0, sizeof(dp[0]));
  for (int i = 0; i < n; i++) {
    for (int j = 1; j < ltrans; j++) dp[i][j] = max(dp[i][j], dp[i][j - 1]);
    memset(rdp, -1, sizeof(rdp));
    rdp[0][arr[i].first] = arr[i].first;
    int now = 0, nxt = 1;
    for (int j = i; j >= 0; j--) {
      for (int k = 0; k < ltrans; k++) rdp[nxt][k] = rdp[now][k];
      for (int k = to[j].first; k <= arr[j].first; k++)
        rdp[nxt][to[j].first] = max(rdp[now][k], rdp[nxt][to[j].first]);
      for (int k = to[j].second - 1,
               maxv = max(rdp[now][to[j].second], to[j].second);
           k >= arr[j].first; k--) {
        for (int t = 0; t < (int)have[k].size(); t++) {
          int no = have[k][t];
          if (to[no].first < arr[j].first && no > j && no <= i)
            rdp[nxt][to[no].first] = max(rdp[nxt][to[no].first], maxv);
        }
        maxv = max(maxv, rdp[now][k]);
        if (k == arr[j].first) rdp[nxt][k] = max1(rdp[nxt][k], maxv);
      }
      swap(now, nxt);
      for (int k = 0; k < ltrans; k++)
        if (rdp[now][k] >= k) {
          dp[i + 1][rdp[now][k]] = max(
              dp[i + 1][rdp[now][k]], dp[j][k] + trans[rdp[now][k]] - trans[k]);
        }
    }
  }
  int ans = 0;
  for (int i = 0; i <= ltrans; i++) ans = max(ans, dp[n][i]);
  cout << ans << endl;
  return 0;
}
