#include<bits/stdc++.h>

using namespace std;

int main()
{
  int n;
  cin>>n;

  vector<pair<int,int>> movie;
  int num[100] = {0};
  
  for(int i = 0;i < n;++i){
    int a,b;
    cin>>a;
    cin>>b;

    movie.push_back(make_pair(a,b));
  }
  sort(movie.begin(),movie.end());

  int sum = 0;
  for(int i = 1;i <= 31;++i){
    int begin = 0;
    int end = 0;
    int place = 0;
    int times = 0;
    int check = 0;

    for(pair<int,int> e : movie){
      if(i >= e.first && i <= e.second){
        if(check == 0){
          begin = e.first;
          end = e.second;
          place = times;
          check = 1;
        }
        else{
          if(num[place] == 1 && num[times] == 0){
            begin = e.first;
            end = e.second;
            place = times;
          }
          else if(num[place] == 0 && num[times] == 0){
            if(end > e.second){
              begin = e.first;
              end = e.second;
              place = times;
            }
          }
        }
      }
      ++times;
    }

    if(num[place] == 0){
      sum += 100;
      num[place] = 1;
    }
    else{
      sum += 50;
    }
  }

  cout<<sum<<endl;

  return 0;
}
