i think i didn't explain correctly

look i have two columns, with numbers, i the second column i introduce values sometime, and those values usually are the same like in first column, if the value is not in the first column i want that cell to be colored in red ( in the second column)
i have to check the second columns (to see if i have those values in the first column) and if i don't have the number in the fist column, then i want the the cell red in the second column,

i cannot introduce formula in the excel ( in cell A) because i have values in that cell,
this should be dome in conditional formatting or in the VBR