#include <bits/stdc++.h>

using namespace std;

#define REP(i,a,b) for(int i=a;i<(int)b;i++)
#define rep(i,n) REP(i,0,n)

int main() {
  
  int N; cin >> N;
  int sum = 0;
  rep(i, N) {
    char ch;
    int H, M, h, m; cin >> H >> ch >> M >> h >> ch >> m;
    if(h < H) { h += 24; }
    sum += (h-H) * 60 + (m-M);
  }
  
  cout << sum << endl;
  
  return 0;
}