#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
using namespace std;

const int N = 2e3 + 5;
const int MAX = 5e5 + 5;
int hash[N],a[MAX];
int main()
{
    int n;
    while(~scanf("%d",&n))
    {
        int HH,MM,H,M,sum = 0;
        sum = 24*60;
        memset(hash,0,sizeof(hash));
        for(int i = 0;i < n;++i){
           scanf("%d:%d",&HH,&MM);
           scanf("%d:%d",&H,&M);
           HH = HH*60 + MM;             //start time
           H = H*60 + M;             // end time
           for(int i = HH;i < H;++i){
              if(!hash[i]){
                 sum--;
                 hash[i] = 1;
              }
           }
        }
        printf("%d\n",sum);
    }
    return 0;
}