#include <cstdio>
#include <algorithm>
#define NMAX 400000

using namespace std;

bool v[NMAX];
int N, K, M, x, y, T;
FILE *f = fopen("stergeri.in", "r"), *g = fopen("stergeri.out", "w");

int main(void)
{
	 fscanf(f, "%d%d%d", &N, &M, &K);
	 for(register int i = 1; i <= M; i++)
	 {
		  fscanf(f, "%d%d", &x, &y);
		  for(register int k = x; k <= y; k++)
		   v[k] = true;
	 }
	 for(register int j = 1; j <= N; j++)
	  if(v[j] == false)
			T++;
			
	 fprintf(g, "%d", T);
	 
	 fclose(f);
	 fclose(g);
	 return 0;
}