#include <bits/stdc++.h>
#define rep(i,n) for(ll (i)=0;(i)<(n);(i)++)
#define repi(i,a,b) for(ll (i)=(a);(i)<(b);(i)++)
#define SIZE_OF_ARRAY(array)    (sizeof(array)/sizeof(array[0]))
typedef long long ll;
using namespace std;
int main(){
  int n;
  cin >> n;
  int H,h,M,m;
  char a,b;
  int sum = 0;
  rep(i,n) {
    cin >> H >> a >> M >> h >> b >> m;
    H = H*60+M;
    h = h*60+m;
    if(H>h){
      sum += ((24*60-H)+h);
    }else{
      sum += (h-H);
    }
  }
  cout << sum << endl;
  return 0;
}