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

int main() {
  int N; cin >> N;
  int ans = 0;
  for(int i = 0; i < N; i++){
    string S, T; cin >> S >> T;
    S += ":", T += ":";
    int s = 0, s1 = 0, s2 = 0, t = 0, t1 = 0, t2 = 0;
    for(int j = 0; j < (int)S.size(); j++){
      if(S[j] != ':'){
        if(s == 0){
          s1 *= 10;
          s1 += S[j]-48;
        }else{
          s2 *= 10;
          s2 += S[j]-48;
        }
      }else{
        s++;
      }
    }
    for(int j = 0; j < (int)T.size(); j++){
      if(T[j] != ':'){
        if(t == 0){
          t1 *= 10;
          t1 += T[j]-48;
        }else{
          t2 *= 10;
          t2 += T[j]-48;
        }
      }else{
        t++;
      }
    }
    int s3 = s1*60+s2, t3 = t1*60+t2;
    if(s3 > t3) t3 += 1440;
    ans += t3-s3;
  }
  cout << ans << endl;
}