#include <stdio.h>

int main(void){
    int i, N, H, M, h, m;
    int t = 0;
    scanf("%d", &N);

    for(i=0;i<N;i++){
        scanf("%d:%d %d:%d", &H, &M, &h, &m);
        if(H>h){
            h += 24;
        }
        t += (h*60+m) - (H*60+M);
    }
    printf("%d\n", t);
    return 0;
}