#include <algorithm>
#include <cstdio>
#include <cstdlib>
#include <cctype>
#include <cmath>
#include <iostream>
#include <queue>
#include <list>
#include <map>
#include <numeric>
#include <set>
#include <sstream>
#include <string>
#include <vector>
using namespace std;
#define REP(i,a,n) for(int i=(a); i<(int)(n); i++)
#define rep(i,n) REP(i,0,n)
#define FOR(it,c) for(__typeof((c).begin()) it=(c).begin(); it!=(c).end(); ++it)
#define ALLOF(c) (c).begin(), (c).end()
typedef long long ll;


int main(){
  int N;
  cin >> N;
  int ret = 0;

  rep(i,N){
    char c;
    int H,M,h,m;
    scanf("%d:%d %d:%d", &H, &M, &h, &m);
    int a = H * 60 + M;
    int b = h * 60 + m;
    if(a > b){
      b += 60 * 24;
    }
    ret += b - a;
  }
  
  cout << ret << endl;
  return 0;
}