#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() #include<cstring> // strcpy()\strcat()\strcmp()\strlen()\memset() #include<cmath> //sqrt()\pow()\abs()\ceil()\floor()\max()\min() using namespace std; int main(){ int i,j,n,m,cnt=0,a[10001]={0},b[10001]={0}; cin>>n>>m; for(i=0;i<m*2;i++){ cin>>a[i]; } for(i=0;i<m*2;i+=2){ for(j=a[i];j<=a[i+1];j++) b[j]=1; } for(i=0;i<n;i++){ if(b[i]==0)cnt++; } cout<<cnt; return 0; }