有没有大佬解释一下

AC代码

#include<iostream>
using namespace std;
long long o;
unsigned long long n;
int main(){
	cin>>o;
	if(o<=0){
		cout<<"0";
	}else {
		n=o;
		n=n*2-1;
		cout<<n;
	}
	return 0;
}

90代码

#include<cstdio>
using namespace std;
long long o;
unsigned long long n;
int main(){
	scanf("%lld",&o);
	if(o<=0){
		printf("0");
	}else {
		n=o;
		n=n*2-1;
		printf("%lld",n);
	}
	return 0;
}