// dfmt off
T lread(T=long)(){return readln.chomp.to!T;}T[] lreads(T=long)(long n){return iota(n).map!((_)=>lread!T).array;}
T[] aryread(T=long)(){return readln.split.to!(T[]);}void arywrite(T)(T a){a.map!text.join(' ').writeln;}
void scan(L...)(ref L A){auto l=readln.split;foreach(i,T;L){A[i]=l[i].to!T;}}alias sread=()=>readln.chomp();
void dprint(L...)(lazy L A){debug{auto l=new string[](L.length);static foreach(i,a;A)l[i]=a.text;arywrite(l);}}
alias PQueue(T,alias l="b<a")=BinaryHeap!(Array!T,l);import std, core.bitop;
// dfmt on
void main()
{
    auto input = stdin.byLine.map!split.joiner;

    long X;
    X = input.front.to!long;
    input.popFront;

    long K;
    K = input.front.to!long;
    input.popFront;

    long D;
    D = input.front.to!long;
    input.popFront;

    solve(X, K, D);
}

void solve(long X, long K, long D)
{
    X = abs(X);
    if (0 <= X - K * D)
    {
        writeln(X - K * D);
        return;
    }
    long c = X / D;
    long x = X - c * D;
    long k = K - c;
    writeln((k & 1) ? abs(x - D) : x);
}
