why minimum possible integer minus one becomes maximum possible integer in c

I know that c works in two’s complement but still i can’t undrstand how the program below gives me 2147483647 as output.

#include<stdio.h>
int main(){

int a=-2147483648;
a-=1;
printf("%d",a);

}

>Solution :

minimum number in twos comlement is 100000…0
if you reduce one from that it means computer will add -1 to it
-1 in twos complement is: 11111…1
so if you add them the answer is 0111111…1
which is maximum integer or 2147483647