"use strict";

process.stdin.resume();
process.stdin.setEncoding('utf8');

var g_input = '';
process.stdin.on('data', function(chunk) {
    g_input += chunk;
});

process.stdin.on('end', function() {
    Main(g_input.split(/\r?\n/));
});

function Main(input) {

    const nmd = input[0].split(' ').map(function(value) { return parseInt(value, 10); });
    const n = nmd[0];
    const m = nmd[1];
    const d = nmd[2];

    let ans = 0;
    if (d === 0) {
        ans = (n * (m - 1)) / Math.pow(n, 2);
    } else {
        ans = (2 * (n - d) * (m - 1)) / Math.pow(n, 2);
    }

    console.log(ans);

    return 0;
}
