请问大佬们怎么想到2e16（65536）这个特殊情况的呀？

#include<bits/stdc++.h>
#define int long long
using namespace std;
string n; 
int ans=0;
signed main(){
	cin>>n;
	for(int i=0;i<=n.size();i++)
	{
		if(n[i]=='1'||n[i]=='2'||n[i]=='4'||n[i]=='8')
		ans++;
		if(n[i]=='6'&&n[i+1]=='5'&&n[i+2]=='5'&&n[i+3]=='3'&&n[i+4]=='6')
		{
			ans++;
			i+=4;
		}
	}
	cout<<ans;
	return 0;
}