using Lib; using ModInt = Lib.StaticModInt; using System; using System.Collections.Generic; using System.Diagnostics; using System.IO; using System.Linq; using System.Runtime.CompilerServices; using System.Text; using static Lib.OutputLib; public class Solver { const bool MultiTestCase = false; void Solve() { int n = ri; long l0 = ri, r0 = ri; ModInt ans = 0; for (int i = 0; i < n - 1; i++) { long l = ri, r = ri; if (r0 < l) ans += 1; else if (r < l0) continue; else { ModInt c = 0; c += Math.Max(0, l - l0) * (r - l + 1); long a = Math.Max(l0, l), b = Math.Min(r, r0 + 1); c += (b - a) * r - (b - a) * (a + b - 1) / 2; c /= r - l + 1; ans += c; } } ans /= r0 - l0 + 1; ans += 1; Write(ans); } #pragma warning disable CS0162 public Solver() { if (!MultiTestCase) Solve(); else for (int t = ri; t > 0; t--) Solve(); } #pragma warning restore CS0162 const int IINF = 1 << 30; const long INF = 1L << 60; int ri { [MethodImpl(256)] get => (int)sc.Integer(); } long rl { [MethodImpl(256)] get => sc.Integer(); } uint rui { [MethodImpl(256)] get => (uint)sc.UInteger(); } ulong rul { [MethodImpl(256)] get => sc.UInteger(); } double rd { [MethodImpl(256)] get => sc.Double(); } string rs { [MethodImpl(256)] get => sc.Scan(); } string rline { [MethodImpl(256)] get => sc.Line(); } public StreamScanner sc = new StreamScanner(Console.OpenStandardInput()); void ReadArray(out int[] a, int n) { a = new int[n]; for (int i = 0; i < a.Length; i++) a[i] = ri; } void ReadArray(out long[] a, int n) { a = new long[n]; for (int i = 0; i < a.Length; i++) a[i] = rl; } void ReadArray(out T[] a, int n, Func read) { a = new T[n]; for (int i = 0; i < a.Length; i++) a[i] = read(); } void ReadArray(out T[] a, int n, Func read) { a = new T[n]; for (int i = 0; i < a.Length; i++) a[i] = read(i); } } static class Program { static public void Main(string[] args) { SourceExpander.Expander.Expand(); Console.SetOut(new StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false }); new Solver(); Console.Out.Flush(); } } #region Expanded by https://github.com/kzrnm/SourceExpander namespace Lib{public partial class StreamScanner{public int[][]ReadUnweightedTree(int n,int origin=1){var gr=new List[n];for(int i=0;i();for(int i=0;i=len){ptr=0;if((len=str.Read(buf,0,1024))<=0){isEof=true;return 0;}}return buf[ptr++];}[MethodImpl(256)]public char Char(){byte b=0;do b=Read();while(b<33||126=33&&b<=126;b=(char)Read())sb.Append(b);return sb.ToString();}[MethodImpl(256)]public long Integer(){long ret=0;byte b=0;var ng=false;do b=Read();while(b!='-'&&(b<'0'||'9'double.Parse(Scan());}} namespace Lib{public interface IStaticMod{uint Mod{get;}bool IsPrime{get;}}public readonly struct Mod1000000007:IStaticMod{public uint Mod=>1000000007;public bool IsPrime=>true;}public readonly struct Mod998244353:IStaticMod{public uint Mod=>998244353;public bool IsPrime=>true;}public readonly struct StaticModInt:IEquatable>where T:struct,IStaticMod{internal readonly uint _v;private static readonly T op=default;public int Value=>(int)_v;public static int Mod=>(int)op.Mod;public static StaticModIntZero=>default;public static StaticModIntOne=>new StaticModInt(1u);[MethodImpl(256)]public static StaticModIntRaw(int v){var u=unchecked((uint)v);return new StaticModInt(u);}[MethodImpl(256)]public StaticModInt(long v):this(Round(v)){}[MethodImpl(256)]public StaticModInt(ulong v):this((uint)(v%op.Mod)){}[MethodImpl(256)]private StaticModInt(uint v)=>_v=v;[MethodImpl(256)]private static uint Round(long v){var x=v%op.Mod;if(x<0)x+=op.Mod;return(uint)x;}[MethodImpl(256)]public static StaticModIntoperator ++(StaticModIntv){var x=v._v+1;if(x==op.Mod)x=0;return new StaticModInt(x);}[MethodImpl(256)]public static StaticModIntoperator --(StaticModIntv){var x=v._v;if(x==0)x=op.Mod;return new StaticModInt(x-1);}[MethodImpl(256)]public static StaticModIntoperator+(StaticModIntlhs,StaticModIntrhs){var v=lhs._v+rhs._v;if(v>=op.Mod)v-=op.Mod;return new StaticModInt(v);}[MethodImpl(256)]public static StaticModIntoperator-(StaticModIntlhs,StaticModIntrhs){unchecked{var v=lhs._v-rhs._v;if(v>=op.Mod)v+=op.Mod;return new StaticModInt(v);}}[MethodImpl(256)]public static StaticModIntoperator*(StaticModIntlhs,StaticModIntrhs)=>new StaticModInt((uint)((ulong)lhs._v*rhs._v%op.Mod));[MethodImpl(256)]public static StaticModIntoperator/(StaticModIntlhs,StaticModIntrhs)=>new StaticModInt((uint)((ulong)lhs._v*Inv(rhs._v)%op.Mod));[MethodImpl(256)]public static StaticModIntoperator+(StaticModIntv)=>v;[MethodImpl(256)]public static StaticModIntoperator-(StaticModIntv)=>new StaticModInt(v._v==0?0:op.Mod-v._v);[MethodImpl(256)]public static bool operator==(StaticModIntlhs,StaticModIntrhs)=>lhs._v==rhs._v;[MethodImpl(256)]public static bool operator!=(StaticModIntlhs,StaticModIntrhs)=>lhs._v!=rhs._v;[MethodImpl(256)]public static implicit operator StaticModInt(int v)=>new StaticModInt(v);[MethodImpl(256)]public static implicit operator StaticModInt(uint v)=>new StaticModInt((long)v);[MethodImpl(256)]public static implicit operator StaticModInt(long v)=>new StaticModInt(v);[MethodImpl(256)]public static implicit operator StaticModInt(ulong v)=>new StaticModInt(v);[MethodImpl(256)]public static implicit operator long(StaticModIntv)=>v._v;[MethodImpl(256)]public static implicit operator ulong(StaticModIntv)=>v._v;[MethodImpl(256)]public StaticModIntPow(long n){var x=this;var r=new StaticModInt(1U);if(n<0)(x,n)=(x.Inv(),-n);while(n>0){if((n&1)>0)r*=x;x*=x;n>>=1;}return r;}[MethodImpl(256)]public StaticModIntInv()=>new StaticModInt(Inv(_v));[MethodImpl(256)]static ulong Inv(ulong x){long u=op.Mod,xu=1,yu=0,v=(long)x,xv=0,yv=1;while(v!=0){long w=SafeMod(u,v);long q=(u-w)/v;long xw=xu-xv*q;long yw=yu-yv*q;u=v;xu=xv;yu=yv;v=w;xv=xw;yv=yw;}return(ulong)(yu<0?yu+op.Mod:yu);}[MethodImpl(256)]static long SafeMod(long x,long m){long r=x%m;if(r<0)r+=m;return r;}[MethodImpl(256)]public override string ToString()=>_v.ToString();[MethodImpl(256)]public string ToString(string format,IFormatProvider formatProvider)=>_v.ToString(format,formatProvider);[MethodImpl(256)]public override bool Equals(object?obj)=>obj is StaticModIntm&&Equals(m);[MethodImpl(256)]public bool Equals(StaticModIntother)=>_v==other._v;[MethodImpl(256)]public override int GetHashCode()=>_v.GetHashCode();}} namespace Lib{public static class OutputLib{[MethodImpl(256)]public static void WriteJoin(string s,IEnumerablet)=>Console.WriteLine(string.Join(s,t));[MethodImpl(256)]public static void WriteMat(T[,]a,string sep=" "){int sz1=a.GetLength(0),sz2=a.GetLength(1);var b=new T[sz2];for(int i=0;i(T[][]a,string sep=" "){for(int i=0;i(T[][]a,Funcmap,string sep=" "){for(int i=0;imap(x)));}[MethodImpl(256)]public static void Write(object t)=>Console.WriteLine(t.ToString());[MethodImpl(256)]public static void Write(params object[]arg)=>Console.WriteLine(string.Join(" ",arg.Select(x=>x.ToString())));[MethodImpl(256)]public static void Write(string str)=>Console.WriteLine(str);[MethodImpl(256)]public static void WriteFlush(object t){Console.WriteLine(t.ToString());Console.Out.Flush();}[MethodImpl(256)]public static void WriteError(object t)=>Console.Error.WriteLine(t.ToString());[MethodImpl(256)]public static void Flush()=>Console.Out.Flush();[MethodImpl(256)]public static void YN(bool t)=>Console.WriteLine(t?"YES":"NO");[MethodImpl(256)]public static void Yn(bool t)=>Console.WriteLine(t?"Yes":"No");[MethodImpl(256)]public static void yn(bool t)=>Console.WriteLine(t?"yes":"no");[MethodImpl(256)]public static void DeleteLine()=>Console.Write("\x1b[1A\x1b[2K");[MethodImpl(256)]public static void ProgressBar(long now,long total,int blocks=50){int x=(int)((2*now*blocks+1)/(2*total));Console.Write($"\x1b[G[\x1b[42m{string.Concat(Enumerable.Repeat("_",x))}\x1b[0m{string.Concat(Enumerable.Repeat("_",blocks-x))}] : {now} / {total}");}}} namespace SourceExpander{public class Expander{[Conditional("EXP")]public static void Expand(string inputFilePath=null,string outputFilePath=null,bool ignoreAnyError=true){}public static string ExpandString(string inputFilePath=null,bool ignoreAnyError=true){return "";}}} #endregion Expanded by https://github.com/kzrnm/SourceExpander