//No.70 睡眠の重要性！＠眠い
import std.stdio;
void main() {
	uint n, total;
	readf("%d\n", &n);
	for(uint i=0; i<n; i++) {
		uint H, M, h, m;
		readf("%d:%d %d:%d\n", &H, &M, &h, &m);
		total += ((24+h)*60 + m) - ((H>12?H:24+H)*60 + M);
	}
	writeln(total);
}