[技巧]读入优化

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