Increment- Decrement Operator in c [duplicate]

This question already has an answer here:

• Why are these constructs (using ++) undefined behavior? 10 answers

#include<stdio.h>
int main()
{
int s=4;
int x=++s+++s;
printf("%d",x);
}

value of x?? Answer should be 12 but i am getting 11. Anyone please explain the concept.