#include <bits/stdc++.h>
using namespace std;

#define reep(i,a,b) for(int i=(a);i<(b);i++)
#define rep(i,n) reep(i,0,(n))

typedef long long ll;

__int128 bigIntMillerRabinSuspectPow(int a, __int128 k, __int128 n){
    __int128 p=1;
    __int128 bit=0x80000000U;
    for(bit=bit*bit*0x40000000U;bit;bit>>=1){
        if(p>1) p=(p*p)%n;
        if(k&bit) p=(p*a)%n;
    }
    return p;
}

int bigIntMillerRabinSuspect(int b, __int128 n){
    __int128 i,t=0,u=n-1;
    __int128 now,next;

    while(!(u&1)) t++,u>>=1;
    now = bigIntMillerRabinSuspectPow(b, u, n);

    for(i=1;i<=t;i++){
        next=(now*now)%n;
        if(next==1 && now!=1 && now!=n-1) return 0;
        now=next;
    }
    return next==1;
}

int bigIntMillerRabin(__int128 n){
    if(n<=1) return 0;
    if(n<=3) return 1;
    if(!(n&1)) return 0;
    if(!bigIntMillerRabinSuspect(2,n)) return 0;
    for(int i=3;i<=201;i+=2) if(!bigIntMillerRabinSuspect(i,n)) return 0;
    return 1;
}

bool prime[100000];

int main(){
    string s;
    cin>>s;
    __int128 n=0;
    rep(i,s.size()){
        n*=10;
        n+=s[i]-'0';
    }
    if(n<10000){
        reep(i,2,100000) prime[i]=true;
        for(int i=2;i*i<=100000;i++){
            if(prime[i]){
                for(int j=i*i;j<100000;j+=i){
                    prime[j]=false;
                }
            }
        }
        ll m=n;
        reep(i,2,m){
            queue<int> q;
            q.push(1);
            vector<bool> used(m+1);
            used[1]=true;
            while(q.size()){
                int top=q.front();
                q.pop();
                // top+1 top-1 top+i top-i
                int next = top+1;
                if(next<=m&&top%i!=0&&!prime[next]&&!used[next]) q.push(next),used[next]=true;
                next = top-1;
                if(0<next&&top%i!=1&&!prime[next]&&!used[next]) q.push(next),used[next]=true;
                next = top+i;
                if(next<=m&&!prime[next]&&!used[next]) q.push(next),used[next]=true;
                next = top-i;
                if(0<next&&!prime[next]&&!used[next]) q.push(next),used[next]=true;
            }
            if(used[m]){
                cout<<i<<endl;
                return 0;
            }
        }
    }
    else{
        if(bigIntMillerRabin(n-8)&&n%8==1){
            cout<<14<<endl;
        }
        else{
            cout<<8<<endl;
        }
    }
}