#include<bits/stdc++.h>
#define endl '\n';
#define rep(i,n) for(int i=0; i<(n); i++)
using namespace std;
using ll = long long;
using P = pair<int,int>;
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("Ofast")
constexpr ll INF = 1e18;
constexpr int inf = 1e9;
constexpr double INFD = 1e100;
constexpr ll mod = 1000000007;
constexpr ll mod2 = 998244353;
const double PI = 3.1415926535897932384626433832795028841971;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
// ios::sync_with_stdio(false);
// cin.tie(nullptr);
// ---------------------------------------------------------------------------

int main(){
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  int N;
  cin >> N;
  int sum = 0;
  for(int i=0; i<N; i++){
    string S,T;
    cin >> S >> T;
    int neru=0,okiru=0;
    while(S.front() != ':'){
      neru *= 10;
      neru += S.front() - '0';
      S.erase(S.begin());
    }
    while(T.front() != ':'){
      okiru *= 10;
      okiru += T.front() - '0';
      T.erase(T.begin());
    }
    S.erase(S.begin());
    T.erase(T.begin());
    neru *= 60;
    okiru *= 60;
    neru += stoi(S);
    okiru += stoi(T);
    if(neru > okiru){
      okiru += 24*60;
    }
    sum += okiru - neru;
  }
  cout << sum << endl;
  return 0;
}