偶数一直减2，奇数减最小质数后一直减2

/*****************************************
Note  :
******************************************/
#include <queue>
#include <math.h>
#include <stack>
#include <stdio.h>
#include <iostream>
#include <vector>
#include <iomanip>
#include <string.h>
#include <algorithm>
#define int long long
#define IL inline
const int N = 1e6+10;
const int INF = 0x3f3f3f3f;
using namespace std;
IL int read()
{
    char ch = getchar();
    int f = 1, num = 0;
    while(ch>'9'||ch<'0')
    {
        if(ch=='-') f = -1;
        ch=getchar();
    }
    while(ch>='0'&&ch<='9')
        num = num*10+ch-'0', ch = getchar();
    return num*f;
}
int n,ans;
signed main()
{
	n=read();
	if(n%2==0)
        printf("%lld\n",n/2);
    else
    {
        int fl=0;
        for(int i = 3;i*i<=n;i++)
            if(n%i==0)
            {
                n-=i,fl=1;
                break;
            }
        if(fl)
            printf("%lld\n",n/2+1);
        else puts("1");
    }
}