#include <algorithm>
#include <cstdio>
#include <iostream>
#include <map>
#include <cmath>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <vector>
#include <stdlib.h>
#include <stdio.h>
#include <bitset>
using namespace std;
#define FOR(I,A,B) for(int I = (A); I < (B); ++I)

int main(){
  int n;
  cin >> n;
  long long ans = 0;
  FOR(i,0,n){
    int a1, a2, b2, b1;
    char c1, c2;
    cin >> a1 >> c1 >> b1 >> a2 >> c2 >> b2;
    a1 *= 60;
    a2 *= 60;
    a1 += b1;
    a2 += b2;
    if(a2 < a1) a2 += 60 * 24;
    ans += a2 - a1;
  }
  cout << ans << endl;
  return 0;
}