Easy to overlook the long type

Most farmers in the long digital time stamp of the type of writing, the habit of using the expression 1000 * 60 * 60 * 31 * 12, may remember plus a 1000 * 60 * 60 * 31 * 12l, but I'm sorry this is wrong expression, since 1000 * 60 * 60 * 31 may already be data type Integer overflow, resulting in how the latter figure is multiplied by plus or l are negative