Is there an explanation for inline operators in “k += c += k += c;”?

What is the explanation for the result from the following operation?

k += c += k += c;

I was trying to understand the output result from the following code:

int k = 10;
int c = 30;
k += c += k += c;
//k=80 instead of 110
//c=70

and currently I am struggling with understanding why the result for "k" is 80. Why is assigning k=40 not working (actually Visual Studio tells me that that value is not being used elsewhere)?

Why is k 80 and not 110?

If I split the operation to:

k+=c;
c+=k;
k+=c;

the result is k=110.

I was trying to look through the CIL, but I am not so profound in interpreting generated CIL and can not get a few details:

 // [11 13 - 11 24]
IL_0001: ldc.i4.s     10
IL_0003: stloc.0      // k
// [12 13 - 12 24]

IL_0004: ldc.i4.s     30

IL_0006: stloc.1      // c
// [13 13 - 13 30]

IL_0007: ldloc.0      // k expect to be 10

IL_0008: ldloc.1      // c

IL_0009: ldloc.0      // k why do we need the second load?

IL_000a: ldloc.1      // c

IL_000b: add          // I expect it to be 40

IL_000c: dup          // What for?

IL_000d: stloc.0      // k - expected to be 40

IL_000e: add

IL_000f: dup          // I presume the “magic” happens here

IL_0010: stloc.1      // c = 70

IL_0011: add

IL_0012: stloc.0      // k = 80???

#c-sharp