#include <iostream>
#include <cstdio>
#include <cstring>
#include <vector>
#include <string>
#include <algorithm>
#include <queue>
using namespace std;
const int maxn = 2000;
struct node{
    int lson,rson;
    bool flag;
    int mid(){
        return (lson+rson)>>1;
    }
}tree[maxn*4];
void pushUp(int rt){
    tree[rt].flag = tree[rt<<1].flag&&tree[rt<<1|1].flag;
}
void build(int L,int R,int rt){
    tree[rt].lson = L;
    tree[rt].rson = R;
    tree[rt].flag = false;
    if(L==R)   return;
    int mid = tree[rt].mid();
    build(L,mid,rt<<1);
    build(mid+1,R,rt<<1|1);
}
void update(int L,int R,int l,int r,int rt){
    if(tree[rt].flag) return;
    if(L <= l && R >= r){
        tree[rt].flag = true;
        return;
    }
    int mid = tree[rt].mid();
    if(L <= mid){
        update(L,R,l,mid,rt<<1);
    }
    if(R > mid){
        update(L,R,mid+1,r,rt<<1|1);
    }
    pushUp(rt);
}
int query(int L,int R,int l,int r,int rt){
    if(tree[rt].flag){
        return r-l+1;
    }
    if(l==r) return 0;
    int mid = tree[rt].mid();
    int ret = 0;
    if(L <= mid) ret += query(L,R,l,mid,rt<<1);
    if(R > mid) ret += query(L,R,mid+1,r,rt<<1|1);
    return ret;
}
int main(){

    int n;
    while(~scanf("%d",&n)){
        build(0,1439,1);
        while(n--){
            int a,b,c,d;
            scanf("%d:%d %d:%d",&a,&b,&c,&d);
            update(a*60+b+1,c*60+d,0,1439,1);
        }
        printf("%d\n",1440-query(0,1439,0,1439,1));
    }
    return 0;
}