Fork() - Two processes accessing the same variable

Question

Why in the output he does only the multiplication that is requested in the parent process and does not the sum of the child process?

Entree:

#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>

int main(void) 
{
    int pvar = 1;
    printf("%d\n", pvar);
    pid_t childpid;
    childpid = fork();
    if (childpid == -1) 
    {
        perror("Errorr");
        return 1;
    }

    if (childpid == 0)
    { 
        pvar += 3;
        printf("I am child %ld\n", (long)getpid());

    }
    /* parent code */
    else
    { 
        pvar = pvar *4;
        printf("I am parent %ld\n", (long)getpid());
        printf ("Valor de pvar - %d\n", pvar);
        wait(0);
    }

    return 0;
}

Exit:

1
I am parent 10419
I am child 10420
4