#include <iostream>
#include <string>
#include <queue>
#include <stack>
#include <algorithm>
#include <list>
#include <vector>
#include <complex>
#include <utility>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <bitset>
#include <ctime>
#include <map>
#include <unordered_map>
#include <set>
#include <unordered_set>
#include <cassert>
#include <cstddef>
#include <iomanip>
#include <numeric>
#include <tuple>
#include <random>

#define REP(i,n) for(long (i)=0;(i)<(n);(i)++)
#define FOR(i,a,b) for(long (i)=(a);(i)<(b);(i)++)
#define RREP(i,a) for(long (i)=(a)-1;(i)>=0;(i)--)
#define FORR(i,a,b) for(long (i)=(a)-1;(i)>=(b);(i)--)
#define MOD 1000000007
#define PI acos(-1.0)
#define DEBUG(C) cout<<C<<endl;
#define PII pair<int,int>
#define PLL pair<long,long>
#define ALL(a) (a).begin(),(a).end()
#define SORT(a) sort((a).begin(),(a).end())
#define RSORT(a) sort((a).begin(),(a).end(),greater<int>())

typedef long long LL;
typedef unsigned long long ULL;

using namespace std;

int main(void){
    int N; cin>>N;
    int hm[N][4];
    REP(i,N){
        scanf("%d:%d %d:%d",&hm[i][0],&hm[i][1],&hm[i][2],&hm[i][3]);
    }
    long ans=0;
    REP(i,N){
        if(hm[i][0]>hm[i][2]){
            ans+=(24-hm[i][0])*60;
            ans+=hm[i][2]*60;
            ans=ans-hm[i][1]+hm[i][3];
        }else if(hm[i][0]<hm[i][2]){
            ans+=(hm[i][2]-hm[i][0])*60;
            ans=ans-hm[i][1]+hm[i][3];
        }else{
            if(hm[i][1]>hm[i][3]){
                ans+=24*60;
                ans-=hm[i][1]-hm[i][3];
            }else{
                ans+=hm[i][3]-hm[i][1];
            }
        }
    }
    cout<<ans<<endl;
}