The Harmonic Mean and the AM-HM Inequality

Cindy and Dorothy are sisters in the same school. One day, they left home at the same time. Cindy walked at speed $v_1.$ during the first half of the time and walked at speed $v_2$ the other half of the time. Dorothy walked at speed $v_1$ during the first half of the distance to the school, and walked at speed $v_2$ the other half of the way. Can you tell who reached the school first if $v_1 \neq v_2?$