读入优化

int read(){
    int sum=0;
    char ch=getchar(),last=' ';
    while (ch<'0'||ch>'9'){
        last=ch;ch=getchar();
    }
    while (ch>='0'&&ch<='9'){
        sum=sum*10+ch-'0';
        ch=getchar();
    }
    if (last=='-') sum*=-1;
    return sum;
}