Graph Coloring · Easy problem

Six tasks $T_0,\dots,T_5$ have these conflicts: ($T_0\&T_1$, $T_0\&T_2$, $T_1\&T_2$, $T_0\&T_3$, $T_3\&T_4$, $T_4\&T_5$), apply the greedy rule in the order $T_3, T_0, T_1, T_2, T_4, T_5$: give each task, in turn, the smallest-numbered block not already used by an earlier task it conflicts with. How many blocks does this particular order use?