#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (n); i++)
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<ll> vll;
typedef vector<int> vi;
typedef vector<vector<int>> vvi;
typedef vector<vector<ll>> vvll;
const ll inf = 1e16;
const ll md = 1000000007;

int main() {
  int n;
  cin>>n;
  int ans;
  rep(i,n){
    int h0,m0,h1,m1;
    scanf("%d:%d%d:%d",&h0,&m0,&h1,&m1);
    ans+=24*60-(h0*60+m0)+(h1*60+m1);
  }
  cout<<ans<<endl;
  return 0;
}