//Normal

#define _GLIBCXX_DEBUG
#define ll long long
#include <bits/stdc++.h>
using namespace std;
using Graph = vector<vector<int>>;

void print(auto a){
  cout << a;
}

void prints(auto a){
  cout << a << " ";
}

void prints(){
  cout << " ";
}

void printl(auto a){
  cout << a << endl;
}

void printl(){
  cout << endl;
}

void fix(int n){
  cout << fixed << setprecision(n);
}

int main(){
  int N; cin >> N;
  
  int sum = 0;
  for(int i = 0; i < N; i++){
    string S, T; cin >> S >> T;
    
    int s1 = (int)S.size();
    int s2 = (int)S.find(":");
    int sums = stoi(S.substr(0,s2))*60 + stoi(S.substr(s2+1, s1));
    
    int t1 = (int)T.size();
    int t2 = (int)T.find(":");
    int sumt = stoi(T.substr(0, t2))*60 + stoi(T.substr(t2+1, t1)) + 1440;
    
    sum += (sumt-sums)%1440;
  }
  
  printl(sum);
  
  return 0;
}