#include <bits/stdc++.h>

using namespace std;
bitset<2000003> a;
int main()
{
    ifstream fin("ciur.in");
    ofstream fout("ciur.out");
    int n,i,j,k=0,r;
    fin>>n;
    a[0]=a[1]=1;
    for(j=4;j<=n;j+=2)
        a[j]=1;
        if(n>=2)
            k=1;
    for(i=3;i*i<=n;i+=2)
        if(a[i]==0)
        {
            for(j=i*i;j<=n;j+=2*i)
                a[j]=1;
        }
    for(i=3;i<=n;i+=2)
        if(a[i]==0)
        k++;
    fout<<k;
    return 0;
}