#include<bits/stdc++.h>
using namespace std;
long long L,n;
int p=50;
int main()
{
	long long ans=210;
	cin>>L;
	if(L<=2) cout<<"-1";
	else if(L==3) cout<<"210";
	else{
		cout<<"1";
		for(int i=1;i<=L-4;++i){
			cout<<"0";
		p=p*10%210;
	}
	printf("%03d\n", p); 
	}
}

赛时代码：

//t2 lcm rp+=INF
#include<bits/stdc++.h>
using namespace std;

int l;
string a[10]={"110","050","080","170","020","200"};

int main()
{
//	freopen("lcm.in","r",stdin);
//	freopen("lcm.out","w",stdout);
	scanf("%d",&l);
	
	if(l<=2)return cout<<-1,0;
	if(l==3)return cout<<210,0;
	for(int i=1;i<=l-3;++i)
	{
		if(i==1)printf("1");
		else printf("0");
	}
	
	if(l%6==3)cout<<a[0];
	if(l%6==4)cout<<a[1];
	if(l%6==5)cout<<a[2];
	if(l%6==0)cout<<a[3];
	if(l%6==1)cout<<a[4];
	if(l%6==2)cout<<a[5];
//	fclose(stdin);
//	fclose(stdout);
	return 0;
}