#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cmath>
#include<cctype>
#include<math.h>
#include<string>
#include<string.h>
#include<stack>
#include<queue>
#include<vector>
#include<utility>
#include<set>
#include<map>
#include<stdlib.h>
#include<iomanip>

using namespace std;

#define ll long long
#define ld long double
#define EPS 0.0000000001
#define INF 1e9
#define LINF (ll)INF*INF
#define MOD 1000000007
#define rep(i,n) for(int i=0;i<(n);i++)
#define loop(i,a,n) for(int i=a;i<(n);i++)
#define all(in) in.begin(),in.end()
#define shosu(x) fixed<<setprecision(x)

#define int ll //!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

typedef vector<int> vi;
typedef vector<string> vs;
typedef pair<int,int> pii;
typedef vector<pii> vp;

int gcd(int a, int b){
    if(b==0) return a;
    return gcd(b,a%b);
}
int lcm(int a, int b){
    return a/gcd(a,b)*b;
}

int f(string s){
    int a = 0, b = 0;
    int i = 0;
    while(s[i] != ':'){
        a *= 10;
        a += s[i]-'0';
        i++;
    }
    i++;
    while(i < s.size()){
        b *= 10;
        b += s[i]-'0';
        i++;
    }
    return a*60+b;
}

signed main(void) {
    int n;
    cin >> n;
    int ans = 0;
    rep(i,n){
        string s;
        cin >> s;
        int a = f(s);
        cin >> s;
        int b = f(s);
        if(a > b){
            b += 24*60;
        }
        ans += b-a;
    }
    cout << ans << endl;
}