#include<iostream> // cin\cout\endl #include<cstdio> //scanf()\printf() using namespace std; int main(){ int l,m,i,sum=0,j; cin>>l>>m; int a[m*2+1],b[l+2]; for(i=0;i<=l;i++){ b[i]=0; } for(i=0;i<m*2;i+=2){ cin>>a[i]>>a[i+1]; } for(i=0;i<m*2;i+=2){ for(j=a[i];j<=a[i+1];j++){ if(b[j]==0){ b[j]=1; } } } for(i=0;i<=l;i++){ if(b[i]==0){ sum++; } } cout<<sum; return 0; }