import std.conv, std.functional, std.range, std.stdio, std.string;
import std.algorithm, std.array, std.bigint, std.complex, std.container, std.math, 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; }
real readReal() { return readToken.to!real; }

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)); }

struct ModInt(int M) {
  int x;
  this(ModInt a) { x = a.x; }
  this(long a) { x = cast(int)(a % M); if (x < 0) x += M; }
  ref ModInt opAssign(long a) { return (this = ModInt(a)); }
  ref ModInt opOpAssign(string op)(ModInt a) {
    static if (op == "+") { x += a.x; if (x >= M) x -= M; }
    else static if (op == "-") { x -= a.x; if (x < 0) x += M; }
    else static if (op == "*") { x = cast(int)((cast(long)(x) * a.x) % M); }
    else static assert(false);
    return this;
  }
  ref ModInt opOpAssign(string op)(long a) {
    static if (op == "^^") {
      ModInt t2 = this, te = ModInt(1);
      for (long e = a; e; e >>= 1) {
        if (e & 1) te *= t2;
        t2 *= t2;
      }
      x = cast(int)(te.x);
      return this;
    } else return mixin("this " ~ op ~ "= ModInt(a)");
  }
  ModInt inv() const {
    int a = x, b = M, y = 1, z = 0, t;
    for (; ; ) {
      t = a / b; a -= t * b;
      if (a == 0) {
        assert(b == 1 || b == -1);
        return ModInt(b * z);
      }
      y -= t * z;
      t = b / a; b -= t * a;
      if (b == 0) {
        assert(a == 1 || a == -1);
        return ModInt(a * y);
      }
      z -= t * y;
    }
  }
  ModInt opUnary(string op)() const if (op == "-") { return ModInt(-x); }
  ModInt opBinary(string op, T)(T a) const { return mixin("ModInt(this) " ~ op ~ "= a"); }
  ModInt opBinaryRight(string op)(long a) const { return mixin("ModInt(a) " ~ op ~ "= this"); }
  string toString() const { return x.to!string; }
}

enum MO = 10L^^9 + 7;
alias Mint = ModInt!MO;

Mint eval(Mint[] f, Mint x) {
  Mint y;
  foreach_reverse (a; f) {
    y = y * x + a;
  }
  return y;
}

enum LIM = 1010;

void main() {
  auto inv = new Mint[LIM];
  inv[1] = 1;
  foreach (i; 2 .. LIM) {
    inv[i] = -Mint(MO / i) * inv[cast(size_t)(MO % i)];
  }
  
  Mint eval(Mint[] f, Mint x) {
    Mint y;
    foreach_reverse (a; f) {
      y = y * x + a;
    }
    return y;
  }
  
  try {
    for (; ; ) {
      const N = readInt();
      auto A = new long[N];
      auto B = new long[N];
      foreach (i; 0 .. N) {
        A[i] = readLong();
        B[i] = readLong();
      }
      
      auto xs = A.dup ~ B.dup;
      xs = xs.sort.uniq.array;
      const len = cast(int)(xs.length) - 1;
      auto dp = new Mint[][][](N, len, N);
      {
        const coef = Mint(B[0] - A[0]).inv;
        foreach (e; 0 .. len) {
          if (A[0] <= xs[e] && xs[e + 1] <= B[0]) {
            dp[0][e][0] = coef;
          }
        }
      }
      foreach (i; 1 .. N) {
        const coef = Mint(B[i] - A[i]).inv;
        if (i % 2 == 0) {
          // >=
          Mint sum;
          foreach_reverse (e; 0 .. len) {
            auto g = new Mint[i + 1];
            foreach (d; 0 .. i) {
              g[d + 1] = dp[i - 1][e][d] * inv[d + 1];
            }
            const y0 = g.eval(Mint(xs[e]));
            const y1 = g.eval(Mint(xs[e + 1]));
            if (A[i] <= xs[e] && xs[e + 1] <= B[i]) {
              foreach (d; 0 .. i) {
                dp[i][e][d + 1] = -g[d + 1];
              }
              dp[i][e][0] += sum + y1;
              dp[i][e][] *= coef;
            }
            sum += y1 - y0;
          }
        } else {
          // <=
          Mint sum;
          foreach (e; 0 .. len) {
            auto g = new Mint[i + 1];
            foreach (d; 0 .. i) {
              g[d + 1] = dp[i - 1][e][d] * inv[d + 1];
            }
            const y0 = g.eval(Mint(xs[e]));
            const y1 = g.eval(Mint(xs[e + 1]));
            if (A[i] <= xs[e] && xs[e + 1] <= B[i]) {
              foreach (d; 0 .. i) {
                dp[i][e][d + 1] = g[d + 1];
              }
              dp[i][e][0] += sum - y0;
              dp[i][e][] *= coef;
            }
            sum += y1 - y0;
          }
        }
      }
      debug {
        writeln("xs = ", xs);
        foreach (i; 0 .. N) {
          foreach (e; 0 .. len) {
            write(dp[i][e][0 .. i + 1], " ");
          }
          writeln();
        }
      }
      
      Mint ans;
      foreach (e; 0 .. len) {
        auto g = new Mint[N + 1];
        foreach (d; 0 .. N) {
          g[d + 1] = dp[N - 1][e][d] * inv[d + 1];
        }
        const y0 = g.eval(Mint(xs[e]));
        const y1 = g.eval(Mint(xs[e + 1]));
        ans += y1 - y0;
      }
      writeln(ans);
    }
  } catch (EOFException e) {
  }
}