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

int main() {
    int n;
    cin>>n;
    bool isp[n+1];
    fill(isp,isp+n+1,true);
    isp[0]=isp[1]=false;
    vector<int> ps;
    for (int i=2;i<=n;i++) if (isp[i]) {
        ps.push_back(i);
        for (int j=i+i;j<=n;j+=i)
            isp[j]=false;
    }
    int dp[n+1];
    fill(dp,dp+n+1,-1);
    dp[0]=0;
    for (int p:ps)
        for (int j=n-p;j>=0;j--) if (dp[j]!=-1)
            dp[j+p]=max(dp[j+p],dp[j]+1);
    cout<<dp[n]<<endl;
    return 0;
}