06: tree outside the school

06: tree outside the school

#include<stdio.h>
#define MAXN 10000+7
char a[MAXN];
int main()
{
	int i,j,len,m,sum=0;
	scanf("%d %d",&len,&m);
	for(i=1;i<=m;i++)
	{
		int left,right;
		scanf("%d %d",&left,&right);
		for(j=left;j<=right;j++)a[j]=1;
	}
	for(i=0;i<=len;i++)
		if(!a[i])sum++;
	printf("%d\n",sum);
	return 0;
}