Bai2.6.c

// Bai 2.6: tinh tong cac so tu nhien khong lon hon n va chia het cho 7
#include <stdio.h>

int main() {
	unsigned int n;
	unsigned long long sum = 0;
	printf("Nhap vao so nguyen duong n: ");
	scanf("%u", &n);
	long i;
	for(i = 7; i <= n; i += 7) {
		sum += i;
	}
	printf("SUM = %llu", sum);
	
	return 0;
}