51nod1421 最大MOD值

#include<cstdio>
#include<cstring>
#include<cctype>
#include<algorithm>
using namespace std;
#define rep(i,s,t) for(int i=s;i<=t;i++)
#define dwn(i,s,t) for(int i=s;i>=t;i--)
#define clr(x,c) memset(x,c,sizeof(x))
int read(){
	int x=0;char c=getchar();
	while(!isdigit(c)) c=getchar();
	while(isdigit(c)) x=x*10+c-‘0‘,c=getchar();
	return x;
} 
const int nmax=2e5+5;
int a[nmax];
int main(){
	int n=read();
	rep(i,1,n) a[i]=read();
	sort(a+1,a+n+1);
	int ans=0,tp;
	rep(i,1,n-1){
		for(int j=a[i]+a[i];j<=a[n]*2;j+=a[i]){
			tp=lower_bound(a+1,a+n+1,j)-a-1;ans=max(ans,a[tp]%a[i]);
		}
	} 
	printf("%d\n",ans);
	return 0; 
}