#include<iostream>
#include<sstream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<string>
#include<vector>
#include<cmath>
#include<set>
#include<map>
#include<stack>
#include<queue>
#include<numeric>
#include<functional>
#include<complex>

using namespace std;
#define BET(a,b,c) ((a)<=(b)&&(b)<(c))
#define FOR(i,n) for(int i=0,i##_end=(int(n));i<i##_end;i++)
#define SZ(x) (int)(x.size())
#define ALL(x) (x).begin(),(x).end()
#define MP make_pair
#define FOR_EACH(it,v) for(__typeof(v.begin()) it=v.begin(),it_end=v.end() ; it != it_end ; it++)
typedef vector<int> VI;
typedef vector<VI> VVI;

int main()
{
    int n;
    cin>>n;
    int ans = 0 ;
    FOR(i,n){
        int H,M,h,m;
        scanf("%d:%d %d:%d",&H,&M,&h,&m);
        int time = (h * 60 + m) - (H * 60 + M);
        time = (time + 24 * 60) % (24 * 60);
        ans += time;
    }
    cout<<ans<<endl;
    return 0;
}