#include <iostream>
#include <math.h>
#include <algorithm>
#include <map>
#include <vector>
using namespace std;

#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rep2(i, d, n) for (int i = d; i < (int)(n); i++)
#define rRep(i,n) for(int i = n; i >= 0; i--)
#define rRep2(i,d,n) for(int i = n; i >= d; i--)
#define forEach(arr) for (auto& it:arr)


int main(void){
    
    int n,sleep = 0;
    cin >> n;
    
    rep(i,n) {
        
        string a,b,a1[2] = {"",""},b1[2] = {"",""};
        int c,d;
        cin >> a >> b;
        vector<string> v1,v2;
        bool f = false;
        
        for(int i = 0; i < a.length(); i++) {
            if(f) a1[1] +=  a[i];
            else {
                if(a[i] == ':') {
                    f = true;
                    continue;
                }
                a1[0] += a[i];
            }
        }
        f = false;
        for(int i = 0; i < b.length(); i++) {
            if(f) b1[1] += b[i];
            else {
                if(b[i] == ':') {
                    f = true;
                    continue;
                }
                b1[0] += b[i];
            }
        }
        
        c = stoi(a1[0]) * 60 + stoi(a1[1]);
        d = stoi(b1[0]) * 60 + stoi(b1[1]);
        if(d < c)d += (24 * 60);
        sleep += d - c;
    }
    
    cout << sleep;
    
    
    
}