#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <queue>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef tuple<int, int, int> TIII;
typedef long long LL;
typedef unsigned long long ULL;

#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

#define MP make_pair
#define MT make_tuple
#define SZ(a) int((a).size())
#define EACH(i,c) for(auto i: c)
#define SORT(c) sort((c).begin(),(c).end())

#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()

const double EPS = 1e-10;
const double PI  = acos(-1.0);

#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

int main() {
	cin.tie(0);
	ios::sync_with_stdio(false);

	int N;
	cin >> N;

	auto f = [&](string s){
		int pos = s.find_first_of(':');
		PII ret;
		ret.first = toInt(s.substr(0, pos));
		ret.second = toInt(s.substr(pos + 1));
		return ret;
	};

	int ret = 0;
	REP(i, N){
		string S, E;
		cin >> S >> E;

		PII tmp;
		tmp.first = f(E).first - f(S).first + 24;
		tmp.second = f(E).second - f(S).second;
		if(tmp.second < 0){
			tmp.first--;
			tmp.second += 60;
		}
		ret += (tmp.first % 24) * 60 + tmp.second;
	}
	cout << ret << endl;


	return 0;
}