#include <bits/stdc++.h>
using namespace std;
bool flag[10000005];
int main()
{
    int n;
    cin >> n;
    memset(flag, 1, sizeof(flag));
    flag[0] = flag[1] = 0;
    int cnt = 0;
    for(int i = 2; i <= n; i++)
    {
    	if (flag[i] == 1)
    	{
    		for (int j = 2; j * i <= n; j++)
    		{
    			flag[i * j] = 0;
    		}
    	}
    }
    for(int i = 1; i <= n; i++)
    {
    	if (flag[i] == 1)
    	{
    		cnt++;
    	}
    }
    cout << cnt;
    return 0;
}

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