#include<bits/stdc++.h>
using namespace std;

#define int long long
#define pb push_back 
#define pf push_front 
#define mp make_pair
#define fr first
#define sc second
#define Rep(i, n) for ( int i = 0 ; i < (n); i++ )
#define All(v) v.begin(), v.end()

typedef pair<int, int> Pii; typedef pair<int, Pii> Pip;
const int INF = 1107110711071107;

struct BiMatch{
  int n;
  vector<vector<int> > G;
  vector<int> match,used;
  
  BiMatch(){}
  BiMatch(int sz):n(sz),G(sz),match(sz),used(sz){}
  
  void add_edge(int u,int v){
    G[u].push_back(v);
    G[v].push_back(u);
  }

  bool dfs(int v){
    used[v]=true;
    for(int i=0;i<(int)G[v].size();i++){
      int u=G[v][i],w=match[u];
      if(w<0||(!used[w]&&dfs(w))){
	match[v]=u;
	match[u]=v;
	return true;
      }
    }
    return false;
  }

  int build(){
    int res=0;
    fill(match.begin(),match.end(),-1);
    for(int v=0;v<n;v++){
      if(match[v]<0){
	fill(used.begin(),used.end(),0);
	if(dfs(v)){
	  res++;
	}
      }
    }
    return res;
  }
};

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

  BiMatch BM(n+32);
  Rep(i, n) {
    int a, b;
    cin >> a >> b;
    a--; b--;
    for ( int j = a; j <= b; j++ ) {
      BM.add_edge(i, n+j);
    }
  }

  cout << 50*31 + 50*BM.build() << endl;
}