#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=2;i<10000;i++){
		if(isp[i])continue;
		if(ans[i])continue;
		queue<int> q;
		int m=0;
		for(int j=1;i+j<10000;j++){
			if(!isp[i+j]&&!ans[i+j]){m=j;q.push(i+j);break;}
		}
		while(q.size()){
			ans[a=q.front()]=m;
			q.pop();
			if(a+1<10000&&!isp[a+1]&&!ans[a+1]){ans[a+1]=m;q.push(a+1);}
			if(a+m<10000&&!isp[a+m]&&!ans[a+m]){ans[a+m]=m;q.push(a+m);}
			if(a-1>1&&!isp[a-1]&&!ans[a-1]){ans[a-1]=m;q.push(a-1);}
			if(a-m>1&&!isp[a-m]&&!ans[a-m]){ans[a-m]=m;q.push(a-m);}
		}
	}
	if(n>=10000)n=5000;
	printf("%d\n",ans[n]); 
	return 0;
}