// O(n*log(n)), drvo struktura e redundantna, max1D range sum e sufficient

#include <stdio.h>
#include <stdlib.h>

struct coek
{
    int time;
    int val;

};

typedef struct coek coek;

int sporedi( const void* prv, const void* vtor)
{
    return( ((coek*)prv)->time - ((coek*)vtor)->time );
}

int main()
{
    int n, h, m, remain, sum, izlez;
    char t;
    scanf("%d", &n);
    coek vreminja[2*n];

    for(int i = 0; i < 2*n; i+=2)
    {
        scanf("%d", &h);
        scanf("%c", &t);
        scanf("%d", &m);
        scanf("%d", &remain);

        /*printf("h:%d\n", h);
        printf("m:%d\n", m);
        printf("r:%d\n", remain);*/

        sum = 60 * h + m;

        vreminja[i].time = sum;
        vreminja[i].val = 1;

        vreminja[i+1].time = sum + remain;
        vreminja[i+1].val = -1;
    }

    qsort((void*)vreminja, 2*n, sizeof(coek), sporedi);

    sum = 0;
    for(int i = 0; i < 2*n; i++)
    {
        //printf("%d ", vreminja[i].time);
        if(sum < 0)
            sum = 0;
        sum += vreminja[i].val;
        if(sum > izlez)
            izlez = sum;
    }

    printf("%d\n", izlez);
    return(0);
}