#include <cstdio>
#include <cstdlib>
#include <cstring>

#include <queue>

using namespace std;


int main(){
	
	char s[31];
	scanf("%s",s);
	int len=strlen(s);
	int n;
	if(len>2){printf("8\n");return 0;}
	else n=atoi(s);
	int isp[10001]={};
	isp[2]=1;
	for(int i=3;i<=n;i+=2)isp[i]=1; 
	for(int i=3;i*i<=n;i+=2){
		if(isp[i])for(int j=i*i;j<=n;j+=i)isp[j]=0;
	} 
	
	int ans[10001]={};
	ans[1]=1;
	int a=0;
	for(int i=1;i<n;i++){
		if(isp[1+i])continue;
		if(ans[1+i])continue;
		queue<int> q;q.push(1+i);
		int b[10001]={};
		while(q.size()){
			if(!ans[a=q.front()])ans[a]=i;
			q.pop();
			if(a+1<=n&&!isp[a+1]&&!b[a+1]){b[a+1]++;q.push(a+1);}
			if(a+i<=n&&!isp[a+i]&&!b[a+i]){b[a+i]++;q.push(a+i);}
			if(a-1>1&&!isp[a-1]&&!b[a-1]){b[a-1]++;q.push(a-1);}
			if(a-i>1&&!isp[a-i]&&!b[a-i]){b[a-i]++;q.push(a-i);}
		}
	}
	/*for(int i=0;i<20;i++){
		if(isp[i])printf("%d ",i);
	}
	for(int i=0;i<20;i++)printf("%d %d \n",ans[i],i);
	*/
	if(n>=10000)n=5000;
	printf("%d\n",ans[n]);
	
	return 0;
}