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#include <iostream>
#include <fstream>
#include <cassert>
using namespace std;
ifstream f("ciur.in");
ofstream g("ciur.out");
bool prim[2000005];
int n;
int main()
{
f >> n;
int nr = 0;
fill(prim+1,prim+n+1,true);
for (long long i = 2;i <= n;i++)
{
if (prim[i])
{
for (long long j = i * i;j <= n;j += i)
prim[j] = false;
nr++;
}
}
g << nr;
f.close();
g.close();
return 0;
}