Dou itashimashite

どういたしまして (dou itashimashite)

ようこそ i think

Yokoso is welcoming someone to a place like a shop, I don't think you can use it in response to a thank you. "Dou itashi mashite" is the most common.

ようこそ = 'yokoso' = mean welcome cbut どういたしまして= ' dou itashimashite ' ＝ u r welcome