BEGIN {first = 1; count = 0}
{
    thisline = $0;
    if (!first) {
	if (thisline != lastline) {
	    printf("%s: %d\n", lastline, count);
	    count = 0;
	}
    }
    else
	first = 0;
    lastline = thisline;
    count++;
}
END { printf("%s: %d\n", lastline, count) }