import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.bitmanip, std.complex, std.container, std.math, std.mathspecial, std.numeric, std.regex, std.typecons;
import core.bitop;

class EOFException : Throwable { this() { super("EOF"); } }
string[] tokens;
string readToken() { for (; tokens.empty; ) { if (stdin.eof) { throw new EOFException; } tokens = readln.split; } auto token = tokens.front; tokens.popFront; return token; }
int readInt() { return readToken.to!int; }
long readLong() { return readToken.to!long; }

string COLOR(string s = "") { return "\x1b[" ~ s ~ "m"; }

bool chmin(T)(ref T t, in T f) { if (t > f) { t = f; return true; } else { return false; } }
bool chmax(T)(ref T t, in T f) { if (t < f) { t = f; return true; } else { return false; } }

int binarySearch(alias pred, T)(in T[] as) { int lo = -1, hi = cast(int)(as.length); for (; lo + 1 < hi; ) { const mid = (lo + hi) >> 1; (unaryFun!pred(as[mid]) ? hi : lo) = mid; } return hi; }
int lowerBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a >= val)); }
int upperBound(T)(in T[] as, T val) { return as.binarySearch!(a => (a > val)); }




void main() {
  try {
    for (; ; ) {
      const N = readInt;
      auto L = new long[N];
      auto R = new long[N];
      foreach (i; 0 .. N) {
        L[i] = readLong;
        R[i] = readLong;
      }
      
      auto ls = L.dup;
      ls.sort;
      long l0;
      foreach (i; 0 .. N) {
        chmax(l0, ls[i] - i);
      }
      debug {
        writeln("ls = ", ls);
        writeln("l0 = ", l0);
      }
      
      // [a, a + N)
      bool check(long a) {
        auto rss = new long[][N];
        foreach (i; 0 .. N) {
          rss[max(L[i] - a, 0)] ~= R[i] - a;
        }
        BinaryHeap!(Array!long, "a > b") que;
        foreach (j; 0 .. N) {
          foreach (r; rss[j]) que.insert(r);
          if (que.empty) return false;
          if (!(j <= que.front)) return false;
          que.removeFront;
        }
        return true;
      }
      
      long lo = l0 - 1, hi = R.maxElement + 1;
      for (; lo + 1 < hi; ) {
        const mid = (lo + hi) / 2;
        (check(mid) ? lo : hi) = mid;
      }
      writeln(lo - l0 + 1);
    }
  } catch (EOFException e) {
  }
}