# include<iostream> # include<cstdio> using namespace std; int main() { int l,m,n1,n2,out = 0; cin>>l>>m; int o[m],f[m],r[l+1]; for(int i = 0; i <= l; i++) { r[i] = 1; } for(int i = 0; i < m; i++) { cin>>n1>>n2; o[i] = n1; f[i] = n2; } for(int a = 0; a < m; a++) { for(int b = o[a]; b <= f[a]; b++) { r[b] = 0; } } for(int i = 0; i <= l; i++) { if(r[i] == 1) { out++; } } printf("%d", out); return 0; }