#include <bits/stdc++.h>
#define rep(i, n) for(long long i = 0; i < (long long)n; i++)
#define ALL(v) (v).begin(), (v).end()
#define rALL(v) (v).rbegin(), (v).rend()
using namespace std;

using lint = long long;
using ld = long double;

int main() {
    int n;
    cin >> n;
    int ans = 0;
    auto calc = [](int a, int b, int c, int d) -> int {
        if (a > c || (a == c && b > d)) {
            c += 24;
        }
        if (b > d) {
            c--;
            d += 60;
        }
        return (c - a) * 60 + (d - b);
    };
    while (n--) {
        string s, t;
        cin >> s >> t;
        int x, y;
        rep(i, (int)s.size()) {
            if (s[i] == ':') {
                x = i;
            }
        }
        rep(i, (int)t.size()) {
            if (t[i] == ':') {
                y = i;
            }
        }
        int a = stoi(s.substr(0, x)), b = stoi(s.substr(x + 1));
        int c = stoi(t.substr(0, y)), d = stoi(t.substr(y + 1));
        ans += calc(a, b, c, d);
    }
    cout << ans << endl;
}