#include <iostream>
#include <fstream>
using namespace std;
long long n,i,d,nr;
char ciur[2000001];
ofstream g("ciur.out");
int main()
{freopen("ciur.in","r",stdin);
scanf("%d",&n);
nr=0;
    ciur[1]=1;
    for ( d = 2; d * d <= n; d++ )
        if ( ciur[d] == 0 )
            {
            for ( i = d * d; i <= n; i = i + d )
                    ciur[i] = 1;}
for(i=2;i<=n;i++)
if(ciur[i]==0)
nr++;
    g<<nr;
    return 0;
}