#include <stdio.h>
int main()
{
	int n,k,l,i,a[100000],b[100000],e;
	double c,d,max=0,f;

	FILE *in,*out;
	in = fopen("input.txt", "r");
	out = fopen("output.txt", "w");

	fscanf(in,"%d",&n);
	fscanf(in,"%d",&k);

	for(i=0 ; i<k ; i++) {
		fscanf(in,"%d %d",&a[i], &b[i]);
	}
	fscanf(in,"%d",&l);
	
	d=l*2+1;

	for(i=0 ; i<k ; i++) {
		if(a[i]==a[i+1]) {
			if(b[i]>b[i+1]) {
				c=a[i]*2-d+b[i]-b[i+1];
			}
			else if(b[i]<b[i+1]) {
				c=a[i]*2-d+b[i+1]-b[i];
			}
		}
		e=l*2+b[k-1]-2;

		if(max<c) {
			max=c;
		}
	}
	
	

	if(max<e) {
		max=e;
	}
	f=max/1;
	if(f=!max) {
		fprintf(out,"%.1f \n",max);
	}
	else {
		fprintf(out,"%.0f \n",max);
	}

	fclose(in);
	fclose(out);
	
	return 0;
}

이게 왜 10점인가요...ㅜㅜ
열심히 해서 풀었는데...