#include <iostream>#include <cstdio>#include <cstdlib>#include <cstring>using namespace std;const int maxn = 1000;int n, month, day, h, m, id, last, god;int presum[maxn][2*maxn], st[maxn], et[maxn], cnt[maxn];char c;int main(){#ifdef LOCAL    freopen("A.in", "r", stdin);#endif    while(scanf("%d", &n)) {        if(n == 0)    break;        last = -1;        memset(cnt, 0, sizeof(cnt));        for(int i = 0; i < n; i++) {            scanf("%d/%d %d:%d %c %d", &month, &day, &h, &m, &c, &id);            if(month*100+day != last || i == n-1) {            //update                    for(int j = 1; j < 1000; j++)                    for(int k = 0; k < god; k++) {                        cnt[j] += presum[j][et[k]?et[k]:1440] - presum[j][st[k]];                    }//                cout <<"Go" << endl;//                cout << presum[3][9*60+10] << endl;//                for(int j = 1; j <= 3; j++)//                    for(int k = 0; k < god; k++)//                    cout << presum[j][et[k]?et[k]:1440] - presum[j][st[k]] << endl;//                for(int i = 1; i <=3 ; i++)//                    cout << cnt[i] << endl;                last = 100*month+day;                god = 0;                memset(presum, 0, sizeof(presum));                memset(et, 0, sizeof(et));            }            if(id == 0)    {                if(c == ‘I‘)    st[god] = h*60+m;                else    et[god++] = h*60+m;                continue;            }            if(c == ‘I‘)                 for(int j = h*60+m; j <= 1440; j++)                    presum[id][j] = j-60*h-m;            else                for(int j = h*60+m+1; j <= 1440; j++)                    presum[id][j] = presum[id][h*60+m];        }        int ans = 0;        for(int i = 1; i < 1000; i++)            ans = max(ans, cnt[i]);        printf("%d\n", ans);    }    return 0;}