C Program to calculate grade based on percentage using If Else statement

Program

#include<stdio.h>
void main()
{
	long int m1, m2, m3, m4, m5, m6;
	long int percent;
	printf("Enter the marks for 6 subjects\n");
	scanf("%ld %ld %ld %ld %ld %ld", &m1, &m2, &m3, &m4, &m5, &m6);
	percent = ((m1 + m2 + m3 + m4 + m5 + m6)*100/600);
	printf("Percentage : %ld\n",percent);
	if(percent >= 90)
		printf("S grade\n");
	else if(percent >= 80 && percent < 90)
		printf("A grade\n");
	else if(percent >= 70 && percent < 80)
		printf("B grade\n");
	else if(percent >= 60 && percent < 70)
		printf("C grade\n");
	else if(percent >= 50 && percent < 80)
		printf("D grade\n");
	else
		printf("Fail\n");
}

Output 1

Enter the marks for 6 subjects
92
90
99
95
89
91
Percentage : 92
S grade

Output 2

Enter the marks for 6 subjects
1
12
65
32
8
33
Percentage : 25
Fail