import std.stdio, std.algorithm, std.string, std.conv, std.array, std.range, std.math;
int read() { return readln.chomp.to!int; }
int[] reads() { return readln.split.to!(int[]); }

void solve(int n, int m, int d) {
    double ans = (){
        if (d == 0)
            return 1.0 / n;
        else
            return 2.0 * (n - d) / n / n;
    }();
    ans *= m - 1;
    writefln("%.10f", ans);
}

void main() {
    int n, m, d; readf("%d %d %d\n", &n,&m,&d);
    solve(n, m, d);
}

unittest {
    solve(2, 3, 1);
    solve(1000000000,180707,0);
}