#include <bits/stdc++.h>
#pragma GCC optimize("O3", "Ofast")
#define int long long
#define ll long long
#define se second
#define fi first
#define pb push_back
#define lf (id<<1)
#define rg ((id<<1)|1)
#define md ((l+r)>>1)
using namespace std;
typedef pair<int,int> pii;
typedef pair<pii,pii> ipii;
const int MAXN = 5e5+10;
const int MAXA = 5e5+10;
const int SQRT = 450;
const ll INF = 1e18;
const int MOD = 1e9+7;
const int LOG = 60;
int sum(int a, int b){ return (a+MOD+b)%MOD; }
void chsum(int &a, int b){ a = sum(a,b); }
int mul(int a, int b){ return (a*b)%MOD; }
void chmul(int &a, int b){ a = mul(a,b); }
void chmn(auto &a, auto b){ a = min(a, b); }
void chmx(auto &a, auto b){ a = max(a, b); }
vector<int> dx = {0, 0, -1, 1};
vector<int> dy = {1, -1, 0, 0};
int x, n, a[MAXN], t[MAXN];
bool p[110][110], dp[110][110][110];
int solve(){
int nw = a[1];
bool can = 1;
for(int i=2; i<=n; i++){
if(abs(a[i-1]-a[i]) > t[i]-t[i-1]) can = 0;
}
if(can) return 1;
for(int j=1; j<=x; j++)
p[1][j] = 1;
for(int i=1; i<=n-1; i++){ // update ke i+1
for(int j=1; j<=x; j++){
if(!p[i][j]) continue;
int tim = t[i+1]-t[i];
if(abs(a[i+1]-a[i]) > tim && abs(a[i+1]-j) > tim) continue;
// i ke i+1
for(int k=max(1ll, j-tim); k<=min(x, j+tim); k++)
p[i+1][k] = 1;
// j ke i+1
for(int k=max(1ll, a[i]-tim); k<=min(x, a[i]+tim); k++)
p[i+1][k] = 1;
}
}
can = 0;
for(int i=1; i<=x; i++) can |= p[n][i];
if(can) return 2;
return 3;
}
signed main(){
ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
cin>>x>>n; vector<pii> vec; vec.pb({-1, -1});
for(int i=1; i<=n; i++) cin>>t[i];
for(int i=1; i<=n; i++){
cin>> a[i];
vec.pb({t[i], a[i]});
}
sort(vec.begin(), vec.end());
for(int i=1; i<=n; i++)
t[i] = vec[i].fi, a[i] = vec[i].se;
cout << solve() << '\n';
}
