#include <bits/stdc++.h>
#define PN 2270

using namespace std;

int N, PC = 0;
int prime[PN] = {0};
int dp[20001] = {0};

int main(void){
    
    cin >> N;
    
    int i, j, k;
    
    prime[PC++] = 2;
    for(i = 3; i <= N; i += 2){
		k = 0;
		for(j = 3; j <= sqrt(i); j += 2){
			if(i % j == 0){
				k = 1;
				break;
			}
		}
		if(k == 0) prime[PC++] = i;
	}
	
	memset(dp, -1, sizeof(dp));
    
    dp[0] = 0;
    for(i = 0; i < PC; ++i){
        for (int j = N; j >= 0; --j){
            k = prime[i] + j;
            if(k <= N && dp[j] != -1){
                dp[k] = (dp[k] < dp[j] + 1) ? dp[j] + 1 : dp[k];
            }
        }
    }
    
    cout << dp[N] << endl;
    
    return 0;
}