#include <iostream>
#include <fstream>
using namespace std;
ifstream in("ciur.in");
ofstream out("ciur.out");
bool v[2000001];
int main()
{int n,i,j,nr=0;
in>>n;
for(i=2;i<=n;i++)
{if(v[i]==0){nr++;
    for(j=2*i;j<=n;j+=i)
        v[j]=1;
}
}
out<<nr;
}