#include <algorithm>
#include <iostream>
#include <cstdio>
#include <map>
#include <numeric>
#include <cmath>
#include <set>
#include <sstream>
#include <string>
#include <vector>
#include <queue>
#include <stack>
#include <complex>
#include <string.h>
#include <unordered_set>
#include <unordered_map>
#include <iomanip>
#include <sys/time.h>
#include <random>
using namespace std;

#define endl '\n'
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define uniq(v) (v).erase(unique((v).begin(), (v).end()), (v).end())

typedef long long ll;
typedef long double lb;
typedef pair<int, int> P;
typedef complex<double> comp;
typedef vector< vector<lb> > matrix;
struct pairhash {
public:
    template<typename T, typename U>
    size_t operator()(const pair<T, U> &x) const {
	size_t seed = hash<T>()(x.first);
	return hash<U>()(x.second) + 0x9e3779b9 + (seed<<6) + (seed>>2);
    }
};
const int inf = 1e9 + 9;
const ll mod = 1e9 + 7;
const double eps = 1e-8;
const double pi = acos(-1);

int n;

P calc_time() {
    string s;
    cin >> s;

    int i = 0;
    int h = 0, m = 0;
    while (s[i] != ':') {
        h = 10 * h + s[i] - '0';
        i++;
    }
    i++;
    while (i < s.size()) {
        m = 10 * m + s[i] - '0';
        i++;
    }
    return P(h, m);
}

int calc() {
    P p0 = calc_time(), p1 = calc_time();
    for (int i = 0; i <= 60 * 24; i++) {
        if (p0 == p1) return i;
        if (p0.second == 59) {
            p0.second = 0;
            p0.first++;
            p0.first %= 24;
        } else {
            p0.second++;
        }
    }
    return 0;
}

int solve() {
    int res = 0;    
    for (int i = 0; i < n; i++) {
        res += calc();
    }
    return res;
}

void input() {
    cin >> n;
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout << fixed << setprecision(15);

    input();
    cout << solve() << endl;
}