{ N=0; j=0; # use -vW=4 or 14
	for (i=1; ; i++) {
		c = substr($0,i,1);
		# look backward for a "new j" > j
		for (k=i-1; k>j; k--) {
			N++
			if (substr($0,k,1) == c) {
				j = k
				break
			}
		}
		if ((i-j) == W) {
			print i, "(" N " loops)"
			next
		}
	}
} # O(N*W)