printf and character dilema

I have:

 #include <stdio.h> 
    int main(void) { 
        printf("%c","ACEGIK"[3] - 1); 
        return 0; 
   }

I know that the result is F, but why?
I don’t understand that [3]-1.

>Solution :

"AGECIK" is an array of chars

you’re taking the third element (counting from 0) "ACEGIK"[3] that’s G

subtracting 1 'G' - 1 and getting character F

[3] is applied to the array

while -1 is applied to character/value got from the array