#include<cstdio>

using namespace std;

int main(){
  int N;
  scanf("%d", &N);
  int ans = 0;
  for (int i = 0; i < N; i++) {
    int H, M, h, m;
    scanf("%d:%d %d:%d", &H, &M, &h, &m);
    m = (h + 24) * 60 + m;
    M = H * 60 + M;
    ans += ((m - M) % 1440);
  }
  printf("%d\n", ans);
  return 0;
}