#include <stdio.h>
#include <string.h>
#include <stdlib.h>

char * buf;

int sum_to_n(int num)
{
	int i,sum=0;
	for(i=1;i<=num;i++)
		sum+=i;
	return sum;
}

void printSum()
{
	char line[10];
	printf("enter a number:\n");
	fgets(line, 10, stdin);
	if(line != NULL)
		strtok(line, "\n");
	sprintf(buf,"sum=%d",sum_to_n(atoi(line)));
	printf("%s\n",buf);
}

int main(void)
{
	printSum();
	return 0;
}