Populating Flexfield segment automatically

Hi all,

we have a DFF with 4 segments the users will select the values for 3 segments , and the fourth segment will automatically populated with values with the combination of three segments .For example if segment values are as follows 1- FR, 2.1001,3.XX then 4th segment should populates as FR1001XX

is there any way we can acheive this?

Thanks,