/+ dub.sdl:
    name "A"
    dependency "dcomp" version=">=0.6.0"
+/

import std.stdio, std.algorithm, std.range, std.conv;
import std.typecons;
import std.bigint;

// import dcomp.foundation, dcomp.scanner;

// import dcomp.container.deque;

int main() {
    auto sc = new Scanner(stdin);
    long n, m, k;
    sc.read(n, m, k); m++;
    long[] a;
    sc.read(a);

    long[] dp = a.dup;
    long[] ndp = new long[n];
    auto deq = Deque!(long[2])();
    foreach (ph; 2..k+1) {
        ndp[] = -(10L^^18);
        deq.clear();
        foreach (i; 0..n) {
            if (deq.length && deq.front[1] == i-m) {
                deq.removeFront();
            }
            if (deq.length) {
                ndp[i] = deq.front[0] + ph * a[i];
            }
            while (deq.length && deq.back[0] <= dp[i]) {
                deq.removeBack();
            }
            deq.insertBack([dp[i], i]);
        }
        dp[] = ndp[];
    }
    writeln(dp.fold!max);
    return 0;
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/foundation.d */
// module dcomp.foundation;
//fold(for old compiler)
static if (__VERSION__ <= 2070) {
    template fold(fun...) if (fun.length >= 1) {
        auto fold(R, S...)(R r, S seed) {
            import std.algorithm : reduce;
            static if (S.length < 2) {
                return reduce!fun(seed, r);
            } else {
                import std.typecons : tuple;
                return reduce!fun(tuple(seed), r);
            }
        }
    }
    unittest {
        import std.stdio;
        auto l = [1, 2, 3, 4, 5];
        assert(l.fold!"a+b"(10) == 25);
    }
}
version (X86) static if (__VERSION__ < 2071) {
    int bsf(ulong v) {
        foreach (i; 0..64) {
            if (v & (1UL << i)) return i;
        }
        return -1;
    }
    int bsr(ulong v) {
        foreach_reverse (i; 0..64) {
            if (v & (1UL << i)) return i;
        }
        return -1;   
    }
    int popcnt(ulong v) {
        int c = 0;
        foreach (i; 0..64) {
            if (v & (1UL << i)) c++;
        }
        return c;
    }
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/container/deque.d */
// module dcomp.container.deque;

struct Deque(T) {
    import core.exception : RangeError;
    import core.memory : GC;
    import std.range : ElementType, isInputRange;
    import std.traits : isImplicitlyConvertible;

    struct Payload {
        T *d;
        size_t st, length, cap;
        @property bool empty() const { return length == 0; }
        alias opDollar = length;
        ref inout(T) opIndex(size_t i) inout {
            version(assert) if (length <= i) throw new RangeError();
            return d[(st+i >= cap) ? (st+i-cap) : st+i];
        }
        private void expand() {
            import std.algorithm : max;
            assert(length == cap);
            auto nc = max(size_t(4), 2*cap);
            T* nd = cast(T*)GC.malloc(nc * T.sizeof);
            foreach (i; 0..length) {
                nd[i] = this[i];
            }
            d = nd; st = 0; cap = nc;
        }
        void clear() {
            st = length = 0;
        }
        void insertFront(T v) {
            if (length == cap) expand();
            if (st == 0) st += cap;
            st--; length++;
            this[0] = v; 
        }
        void insertBack(T v) {
            if (length == cap) expand();
            length++;
            this[length-1] = v; 
        }
        void removeFront() {
            assert(!empty, "Deque.removeFront: Deque is empty");        
            st++; length--;
            if (st == cap) st = 0;
        }
        void removeBack() {
            assert(!empty, "Deque.removeBack: Deque is empty");        
            length--;
        }        
    }
    struct RangeT(A) {
        alias T = typeof(*(A.p));
        alias E = typeof(A.p.d[0]);
        T *p;
        size_t a, b;
        @property bool empty() const { return b <= a; }
        @property size_t length() const { return b-a; }
        @property RangeT save() { return RangeT(p, a, b); }
        @property RangeT!(const A) save() const {
            return typeof(return)(p, a, b);
        }
        alias opDollar = length;
        @property ref inout(E) front() inout { return (*p)[a]; }
        @property ref inout(E) back() inout { return (*p)[b-1]; }
        void popFront() {
            version(assert) if (empty) throw new RangeError();
            a++;
        }
        void popBack() {
            version(assert) if (empty) throw new RangeError();
            b--;
        }
        ref inout(E) opIndex(size_t i) inout { return (*p)[i]; }
        RangeT opSlice() { return this.save; }
        RangeT opSlice(size_t i, size_t j) {
            version(assert) if (i > j || a + j > b) throw new RangeError();
            return typeof(return)(p, a+i, a+j);
        }
        RangeT!(const A) opSlice() const { return this.save; }
        RangeT!(const A) opSlice(size_t i, size_t j) const {
            version(assert) if (i > j || a + j > b) throw new RangeError();
            return typeof(return)(p, a+i, a+j);
        }
    }
    
    alias Range = RangeT!Deque;
    alias ConstRange = RangeT!(const Deque);
    alias ImmutableRange = RangeT!(immutable Deque);

    Payload *p;
    private void I() { if (!p) p = new Payload(); }
    private void C() const {
        version(assert) if (!p) throw new RangeError();
    }
    //some value
    this(U)(U[] values...) if (isImplicitlyConvertible!(U, T)) {I;
        p = new Payload();
        foreach (v; values) {
            insertBack(v);
        }
    }
    //range
    this(Range)(Range r)
    if (isInputRange!Range &&
    isImplicitlyConvertible!(ElementType!Range, T) &&
    !is(Range == T[])) {I;
        p = new Payload();
        foreach (v; r) {
            insertBack(v);
        }
    }
    
    @property bool empty() const { return (!p || p.empty); }
    @property size_t length() const { return (p ? p.length : 0); }
    alias opDollar = length;
    ref inout(T) opIndex(size_t i) inout {C; return (*p)[i]; }
    ref inout(T) front() inout {C; return (*p)[0]; }
    ref inout(T) back() inout {C; return (*p)[$-1]; }
    void clear() { if (p) p.clear(); }
    void insertFront(T v) {I; p.insertFront(v); }
    void insertBack(T v) {I; p.insertBack(v); }
    void removeFront() {C; p.removeFront(); }
    void removeBack() {C; p.removeBack(); }
    Range opSlice() {I; return Range(p, 0, length); }
}

unittest {
    import std.algorithm : equal;
    import std.range.primitives : isRandomAccessRange;
    import std.container.util : make;
    auto q = make!(Deque!int);
    assert(isRandomAccessRange!(typeof(q[])));

    //insert,remove
    assert(equal(q[], new int[](0)));
    q.insertBack(1);
    assert(equal(q[], [1]));
    q.insertBack(2);
    assert(equal(q[], [1, 2]));
    q.insertFront(3);
    assert(equal(q[], [3, 1, 2]) && q.front == 3);
    q.removeFront;
    assert(equal(q[], [1, 2]) && q.length == 2);
    q.insertBack(4);
    assert(equal(q[], [1, 2, 4]) && q.front == 1 && q.back == 4 && q[$-1] == 4);
    q.insertFront(5);
    assert(equal(q[], [5, 1, 2, 4]));

    //range
    assert(equal(q[][1..3], [1, 2]));
    assert(equal(q[][][][], q[]));
    //const range
    const auto rng = q[];
    assert(rng.front == 5 && rng.back == 4);
    
    //reference type
    auto q2 = q;
    q2.insertBack(6);
    q2.insertFront(7);
    assert(equal(q[], q2[]) && q.length == q2.length);

    //construct with make
    auto a = make!(Deque!int)(1, 2, 3);
    auto b = make!(Deque!int)([1, 2, 3]);
    assert(equal(a[], b[]));
}

unittest {
    import std.algorithm : equal;
    import std.range.primitives : isRandomAccessRange;
    import std.container.util : make;
    auto q = make!(Deque!int);
    q.clear();
    assert(equal(q[], new int[0]));
    foreach (i; 0..100) {
        q.insertBack(1);
        q.insertBack(2);
        q.insertBack(3);
        q.insertBack(4);
        q.insertBack(5);    
        assert(equal(q[], [1,2,3,4,5]));
        q.clear();
        assert(equal(q[], new int[0]));
    }

}
unittest {
    Deque!int a;
    Deque!int b;
    a.insertFront(2);
    assert(b.length == 0);
}

unittest {
    import std.algorithm : equal;
    import std.range : iota;
    Deque!int a;
    foreach (i; 0..100) {
        a.insertBack(i);
    }
    assert(equal(a[], iota(100)));
}
/* IMPORT /home/yosupo/Program/dcomp/source/dcomp/scanner.d */
// module dcomp.scanner;

class Scanner {
    import std.stdio : File;
    import std.conv : to;
    import std.range : front, popFront, array, ElementType;
    import std.array : split;
    import std.traits : isSomeChar, isStaticArray, isArray; 
    import std.algorithm : map;
    File f;
    this(File f) {
        this.f = f;
    }
    char[512] lineBuf;
    char[] line;
    private bool succ() {
        import std.range.primitives : empty, front, popFront;
        import std.ascii : isWhite;
        while (true) {
            while (!line.empty && line.front.isWhite) {
                line.popFront;
            }
            if (!line.empty) break;
            if (f.eof) return false;
            line = lineBuf[];
            f.readln(line);
        }
        return true;
    }

    private bool readSingle(T)(ref T x) {
        import std.algorithm : findSplitBefore;
        import std.string : strip;
        import std.conv : parse;
        if (!succ()) return false;
        static if (isArray!T) {
            alias E = ElementType!T;
            static if (isSomeChar!E) {
                //string or char[10] etc
                //todo optimize
                auto r = line.findSplitBefore(" ");
                x = r[0].strip.dup;
                line = r[1];
            } else {
                auto buf = line.split.map!(to!E).array;
                static if (isStaticArray!T) {
                    //static
                    assert(buf.length == T.length);
                }
                x = buf;
                line.length = 0;
            }
        } else {
            x = line.parse!T;
        }
        return true;
    }
    int read(T, Args...)(ref T x, auto ref Args args) {
        if (!readSingle(x)) return 0;
        static if (args.length == 0) {
            return 1;
        } else {
            return 1 + read(args);
        }
    }
}



unittest {
    import std.path : buildPath;
    import std.file : tempDir;
    import std.algorithm : equal;
    import std.stdio : File;
    string fileName = buildPath(tempDir, "kyuridenanmaida.txt");
    auto fout = File(fileName, "w");
    fout.writeln("1 2 3");
    fout.writeln("ab cde");
    fout.writeln("1.0 1.0 2.0");
    fout.close;
    Scanner sc = new Scanner(File(fileName, "r"));
    int a;
    int[2] b;
    char[2] c;
    string d;
    double e;
    double[] f;
    sc.read(a, b, c, d, e, f);
    assert(a == 1);
    assert(equal(b[], [2, 3]));
    assert(equal(c[], "ab"));
    assert(equal(d, "cde"));
    assert(e == 1.0);
    assert(equal(f, [1.0, 2.0]));
}

unittest {
    import std.path : buildPath;
    import std.file : tempDir;
    import std.algorithm : equal;
    import std.stdio : File, writeln;
    import std.datetime;
    string fileName = buildPath(tempDir, "kyuridenanmaida.txt");
    auto fout = File(fileName, "w");
    foreach (i; 0..1_000_000) {
        fout.writeln(3*i, " ", 3*i+1, " ", 3*i+2);
    }
    fout.close;
    writeln("Scanner Speed Test(3*1,000,000 int)");
    StopWatch sw;
    sw.start;
    Scanner sc = new Scanner(File(fileName, "r"));
    foreach (i; 0..500_000) {
        int a, b, c;
        sc.read(a, b, c);
        assert(a == 3*i);
        assert(b == 3*i+1);
        assert(c == 3*i+2);
    }
    foreach (i; 500_000..700_000) {
        int[3] d;
        sc.read(d);
        int a = d[0], b = d[1], c = d[2];
        assert(a == 3*i);
        assert(b == 3*i+1);
        assert(c == 3*i+2);
    }
    foreach (i; 700_000..1_000_000) {
        int[] d;
        sc.read(d);
        assert(d.length == 3);
        int a = d[0], b = d[1], c = d[2];
        assert(a == 3*i);
        assert(b == 3*i+1);
        assert(c == 3*i+2);
    }
    writeln(sw.peek.msecs, "ms");
}


Measured memory_bytes: 7096