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