#include <bits/stdc++.h>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
int n,v[2000001],nr;
int main()
{f>>n;
v[0]=1;
v[1]=1;
for(int i=2;i*i<=n;i+=2)
{int c=i;
if(v[i]==0)
{
while(c<=n)
{c=c+i;
v[c]=1;
}
if(i==2)
    i--;
}
}
for(int i=1;i<=n;i++)
    if(v[i]==0)
    nr++;
g<<nr;
     return 0;
}