HDU - 2206

#include <stdio.h>  
char str[102];  
int ok;  
  
int check(char ch)
{   
    if(ch >= '0' && ch <= '9') 
	{
		return 1;
	}
    if(ch == '.')                   
	{                               
		return 2;                    
	}  
    return 0;  
}  
  
int main()
{  
    int dot, dignum, a, dotsum;  
    while(gets(str))
	{  
        dotsum = a = dot = dignum = 0;  
        for(int i = 0; str[i]; ++i)
		{  
            ok = check(str[i]);  
            if(!ok) 
			{
				break;
			}
            if(ok == 1)
			{  
                dot = 0;  
                ++dignum;  
                a = a * 10 + str[i] - '0';  
                if(dignum > 3 || a > 255)
				{  
                    ok = 0; break;  
                }  
            }
			else
			{  
                dignum = a = 0;  
                ++dot; ++dotsum;  
                if(dot > 1 || dotsum > 3)
				{  
                    ok = 0; break;  
                }  
            }  
        }  
        if(str[0] == '.' || dot || dotsum != 3) 
		{
			ok = 0;
		}  
		printf(ok ? "YES\n" : "NO\n");  
	}  
    return 0;  
}