Decreasing chance of choosing a number from a list of consecutive numbers

Say for example I am given the number 3. I then have to choose a random number from 0 to 3, but where 0 has a bigger chance of being chosen than 1, 1 has a bigger chance of being chosen than 2, and 2 has a bigger chance of being chosen than 3.

I already know that a percentage chance of choosing a specific number from 0 to 3 can kind of be achieved by doing the following:

double r = Math.random();
int n = 0;
if (r < 0.5) {
    n = 0;
    // 50% chance of being 0
} else if (r < 0.8) {
    n = 1;
    // 30% chance of being 1
} else if (r < 0.95) {
    n = 2;
    // 15% chance of being 2
} else {
    n = 3;
    // 5% chance of being 3
}

The problem is that the 3 can be anything. How can I do this?

Note: The numbers 0.5, 0.8 and 0.95 were randomly chosen by me. I would probably expect those numbers to be spread evenly, if that is possible in some way.