import std.stdio,
       std.conv,
       std.string,
       std.range,
       std.math,
       std.algorithm;

void main()
{
    auto N = readln.strip.to!int;
    int[] H, M, h, m;
    foreach (_; 0 .. N)
    {
        auto input = readln.strip.replace(":", " ").split.to!(int[]);
        H ~= input[0];
        M ~= input[1];
        h ~= input[2];
        m ~= input[3];
    }

    int ans;
    foreach (i; 0 .. N)
    {
        auto sleepin = H[i] * 60 + M[i];
        auto wakeup = h[i] * 60 + m[i];
        ans += (1440 + wakeup - sleepin) % 1440;
    }
    ans.writeln;
}