#include <bits/stdc++.h>
#define PB push_back
#define MP make_pair
#define REP(i,n) for (int i=0;i<(n);i++)
#define FOR(i,a,b) for(int i=(a);i<(b);i++)
#define ALL(a) (a).begin(),(a).end()
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> P;
const int INF=1e9;
int main(){
      int n,h1,m1,h2,m2;char com;
      cin>>n;
      int ans=0;
      REP(i,n){
            cin>>h1>>com>>m1>>h2>>com>>m2;
            int t1=h1*60+m1,t2=h2*60+m2;
            if(t2<t1)t2+=(24*60);
            ans+=(t2-t1);
      }
      cout<<ans<<endl;
}