只能判断一次，不能重复判断

# include <stdio.h>
int main()
{
	int c, n0 = 0;
	while((c = getchar())!=EOF)
	{
		if(c != ' ')
		putchar(c);
		if(c == ' ')
			{
			n0++;
				if(n0 <= 1)
				putchar(c);
			}
	}
}