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