Chilly Willy

http://codeforces.com/problemset/problem/248/B

一道规律题，如果模拟的话，会严重超时~

输入n,输出一个数是2，3，5，7的倍数，这个数的位数必须是n;

#include <iostream>using namespace std;int main(){  int n;  while(cin>>n)  {  if(n<3){ cout<<"-1"<<endl;continue; } if(n==3){ cout<<"210"<<endl;continue; }    int s;  s=(n-3)%6;    cout<<"1";for(int i=1;i<n-3;i++) cout<<"0";    if(s==0){cout<<"110"<<endl;continue;}if(s==1){cout<<"050"<<endl;continue;}if(s==2){cout<<"080"<<endl;continue;}if(s==3){cout<<"170"<<endl;continue;}if(s==4){cout<<"020"<<endl;continue;}if(s==5){cout<<"200"<<endl;continue;}   }return 0;}