大神，求助啊。怎么输入负数时是输出B? 要怎么改呢？

#include<stdio.h>
int main()
{
int grade;
printf("请输入你的成绩：");
scanf("%d",&grade);
if (grade>=90&&grade<=100) printf("A\n");
else if(grade<90)
printf("B\n");
else if(grade<80)
printf("C\n");
else if(grade<70)
printf("D\n");
else if(grade<60&&grade>=0)
printf("E\n");
else printf("你输入错误！\n");
return 0;
}