#include <bits/stdc++.h>
using namespace std;
ifstream fin("ciur.in");
ofstream fout("ciur.out");
bool v[2000005];
int main()
{
    int n,i,j,x,k=1;
    fin>>n;
    for (i=3;i*i<=n;i+=2)
        if (v[i]==0)
            for (j=i*i;j<=n;j+=i)
                v[j]=1;
    for (i=3;i<=n;i+=2)
        if(v[i]==0)
            k++;
    fout<<k;
    return 0;
}