//include
#include<bits/stdc++.h>

//using
using namespace std;

//define static const typedef
#define FOR(i, s, n) for(int (i) = (s); (i) < (n); (i)++)
#define REP(i, n) FOR((i), 0, (n))
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SORT(a) sort(ALL(a))
#define RSORT(a) sort(RALL(a))
#define DUMP(x) cerr << #x << " = " << x << "\n";
#define DEBUG(x) cerr << #x << " = " << x << " (L:" << __LINE__ << ") " << __FILE__ << "\n";
#define F first
#define S second

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef vector<PII> VPII;
typedef long long LL;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef unsigned long long ULL;

static const int INF = 1 << 25;
int n, ans = 0, a, b, a1, a2, b1, b2;

int main(){
  scanf("%d", &n);
  for (int i = 0; i < n; ++i)
    {
      scanf("%d:%d %d:%d", &a1, &a2, &b1, &b2);
      a = a1 * 60 + a2;
      b = b1 * 60 + b2;
      if (a > b){
	b += 60 * 24;
      }
      ans += b - a;
    }
  printf("%d\n", ans);
    return 0;
}