#include <fstream>
using namespace std;

ifstream f("ciur.in");
ofstream g("ciur.out");

int n,t;
char v[2000001];

void ciur()
{int i,j;
    t=1;
for(i=3;i<=n;i+=2)
{v[i+1]=1;

if(v[i]==0)
{
    for(j=2*i;j<=n;j+=i)
    v[j]=1;
    t++;
}
}
}

int main()
{f>>n;
ciur();
g<<t;

return 0;
}