#include <bits/stdc++.h>

using namespace std;
bool prim[2000001]={1};
int contor;
int main()
{
    int n,i,j;
    cin>>n;
    for(i=2;i<=n;i++)
        if(prim[i])
    {
        contor++;
        for(j=i+i;j<=n;j=j+i)
        {
            prim[j]=0;
        }
    }
    cout<<contor;
    return 0;
}