#include <iostream>
using namespace std;
int main()
{
int n,m;
scanf("%d %d",&n,&m);
int a[n+5] = {0};
for(int i=0;i<m;i++)
{
int x,y;
scanf("%d %d",&x,&y);
for(int j=x;j<=y;j++)
a[j] = 1;
}
int ans = 0;
for(int i=0;i<=n;i++)
if(!a[i]) ans++;
printf("%d",ans);
return 0;
}
kbz
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