模板——BigInteger

 #include <iostream>
 #include <cstring>
 #include <string>
 #include <vector>
 #include <set>
 #include <cstdio>
 #include <algorithm>
 using namespace std;
 typedef long long LL;

 struct Bign
 {
     static const int BASE=;
     static const int WIDTH=;
     vector<int>s;

     Bign(LL n=){*this=n;}
     Bign(const string& str){*this=str;}
     Bign operator =(LL n)
     {
         s.clear();
         do
         {
             s.push_back(n%BASE);
             n/=BASE;
         }while(n>);
         return *this;
     }
     Bign operator =(const string& str)
     {
         s.clear();
         int x,len=(str.length()-)/WIDTH+;
         for(int i=;i<len;i++)
         {
             int end=str.length()-i*WIDTH;
             int start=max(,end-WIDTH);
             sscanf(str.substr(start,end-start).c_str(),"%d",&x);
             s.push_back(x);
         }
         return *this;
     }
     Bign operator +(const Bign& b)const
     {
         int len1=s.size(),len2=b.s.size();
         int len=max(len1,len2);
         int ans=;
         Bign c;c.s.clear();
         for(int i=;i<len||ans!=;i++)
         {
             if(i<len1) ans+=s[i];
             if(i<len2) ans+=b.s[i];
             c.s.push_back(ans%BASE);
             ans/=BASE;
         }
         return c;
     }
     Bign operator -(const Bign& b)const
     {

         int len1=s.size(),len2=b.s.size();
         Bign c;c.s.clear();
         int ans=,t=;
         for(int i=;i<len1;i++)
         {
             if(i<len2) ans=s[i]-b.s[i]+t;
             else ans=s[i]+t;
             if(ans<)
             {
                 ans+=BASE;t=-;
             }
             else t=;
             if(ans>)c.s.push_back(ans);
         }
         return c;
     }
     Bign operator *(const Bign& b)const
     {
         Bign c;
         int len1=s.size(),len2=b.s.size();
         for(int i=;i<len2;i++)
         {
             for(int j=;j<len1;j++)
             {
                 Bign ans=(LL)b.s[i]*s[j];
                 for(int k=;k<i+j;k++)
                 ans.s.insert(ans.s.begin(),);
                 c=c+ans;
             }
         }
         return c;
     }

     bool operator <(const Bign& b)const
     {
         if(s.size()!=b.s.size()) return s.size()<b.s.size();
         for(int i=s.size()-;i>=;i--)
             if(s[i]!=b.s[i]) return s[i]<b.s[i];
         return false;
     }
     bool operator ==(const Bign& b)const
     {
         if(s.size()!=b.s.size()) return false;
         for(int i=s.size()-;i>=;i--)
             if(s[i]!=b.s[i]) return false;
         return true;
     }
 };
 ostream& operator <<(ostream& out,const Bign& a)
 {
     out<<a.s.back();
     char buf[];
     int len=a.s.size();
     for(int i=len-;i>=;i--)
     {
         sprintf(buf,"%08d",a.s[i]);
         out<<buf;
     }
     return out;
 }
 LL BtoL(const Bign& a)
 {
     LL c;
     char buf[];
     string ss="";
     int len=a.s.size();
     sprintf(buf,"%d",a.s.back());ss+=(string)buf;
     for(int i=len-;i>=;i--)
     {
         sprintf(buf,"%08d",a.s[i]);
         ss+=(string)buf;
     }
     sscanf(ss.c_str(),"%lld",&c);
     return c;
 }
 istream& operator >>(istream& in,Bign& a)
 {
     string s;
     in>>s;
     a=s;
     return in;
 }