Hello, codeforces!

As I am currently learning C in my computer science classes, I was thinking about trying to solve fundamental 800-1000 problems in C in codeforces.

But... I have no idea why this is happening :

#include <stdio.h>

int main()
{
    size_t n;
    scanf("%zu", &n);
    printf("%zu", n);
}

As a custom invocation, it is giving 1 as input gives 2 as output. It gave me random values in other contexts. It seems to behave fine when I use "%ld" instead of "%zu".

Any idea why this happens?