import std.stdio, std.string, std.algorithm, std.array, std.range, std.conv,
    std.typecons, std.math, std.container, std.format, std.numeric;

void main(string[] args)
{
    string s = readln.strip;
    string t = readln.strip;

    long cnt = 0;
    foreach (i; 0 .. s.length)
    {
        if (s[i] != t[i])
        {
            cnt++;
        }
    }
    writeln(cnt);
}
