好多种版本，今天给出其中之一，也是比较快的一种。 

int read() {
	char ch = getchar();
	int num = 0;
	bool fl = 0;
	for(; !isdigit(ch); ch = getchar())
		if (ch=='-') fl = 1;
	for(; isdigit(ch); ch = getchar())
		num = (num<<1)+(num<<3)+ch-48;
	if(fl) num = -num;
	return num;
}
inline int read() {
    char ch = getchar(); int x = 0, f = 1;
    while(ch < '0' || ch > '9') {
        if(ch == '-') f = -1;
        ch = getchar();
    } while('0' <= ch && ch <= '9') {
        x = x * 10 + ch - '0';
        ch = getchar();
    } return x * f;
}

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