#include<bits/stdc++.h>using namespace std;#define maxn 1000000int n,m,x,y,z,ans;struct TreeType{    int l,r,f,w;}tree[maxn<<2];void tree_up(int k) { tree[k].w=tree[k<<1|1].w+tree[k<<1].w; }void tree_down(int k){    tree[k<<1].f+=tree[k].f;    tree[k<<1|1].f+=tree[k].f;    tree[k<<1].w+=(tree[k<<1].r-tree[k<<1].l+1)*tree[k<<1].f;    tree[k<<1|1].w+=(tree[k<<1|1].r-tree[k<<1|1].l+1)*tree[k<<1|1].f;    tree[k].f=0; }void tree_build(int l,int r,int k){    tree[k].l=l; tree[k].r=r;    if(l==r)    {        tree[k].w=1;        return ;    }    int mid=(tree[k].l+tree[k].r)>>1;    tree_build(l,mid,k<<1);    tree_build(mid+1,r,k<<1|1);    tree_up(k);}void tree_change(int l,int r,int k,int x){    if(tree[k].l==l&&tree[k].r==r)    {        tree[k].w+=(tree[k].r-tree[k].l+1)*x;        tree[k].f+=x;        tree_down(k);        return ;     }    if(tree[k].f) tree_down(k);    int mid=(tree[k].l+tree[k].r)>>1;    if(l>mid)  tree_change(l,r,k<<1|1,x);    else if(r<=mid) tree_change(l,r,k<<1,x);    else {        tree_change(l,mid,k<<1,x);        tree_change(mid+1,r,k<<1|1,x);    }}int tree_find(int k,int to){    if(tree[k].l==tree[k].r)    return tree[k].w;    if(tree[k].f) tree_down(k);    int mid=(tree[k].r+tree[k].l)/2;    if(to>mid) return tree_find(k*2+1,to);    else return tree_find(k*2,to);}int main(){    scanf("%d%d",&n,&m);    tree_build(0,n,1);    for(int i=1;i<=m;i++)    {        scanf("%d%d",&x,&y);        tree_change(x,y,1,-1);    }    for(int i=0;i<=n;i++)        if(tree_find(1,i)>0) ans++;    cout<<ans;    return 0;}