#include <cstdio>
#include <iostream>
#include <string>
#include <sstream>
#include <stack>
#include <algorithm>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <cstdlib>
#include <bitset>
#include <tuple>
#include <assert.h>
#include <deque>
#include <bitset>
#include <iomanip>
#include <limits>
#include <chrono>
#include <random>
#include <array>
#include <unordered_map>
#include <functional>
#include <complex>
#include <numeric>
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<class T> inline bool chmin(T& a, T b) { if (a > b) { a = b; return 1; } return 0; }
//constexpr long long MAX = 5100000;
constexpr long long INF = 1LL << 60;
constexpr int inf = 1000000007;
constexpr long long mod = 1000000007LL;
//constexpr long long mod = 998244353LL;
const long double PI = acos((long double)(-1));

using namespace std;
typedef unsigned long long ull;
typedef long long ll;
typedef long double ld;

int main()
{
    /*
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    */
    int res = 0;
    int kkt; scanf("%d", &kkt);
    while (kkt--) {
        int a, b, c, d; scanf("%d:%d", &a, &b);
        scanf("%d:%d", &c, &d);
        if (a < c or (a == c and b < d)) {
            int t2 = c * 60 + d;
            int t1 = a * 60 + b;
            res += t2 - t1;
        }
        else {
            int t2 = c * 60 + d;
            int t1 = a * 60 + b;
            res += t2 + 24 * 60 - t1;
        }
    }
    cout << res << endl;
    return 0;
}