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#include <cstdio>
#include <bitset>
#define NMAX 2000010
using namespace std;
bitset<NMAX> Ciur;
int Solve(int N)
{
if(N<2)
return 0;
if(N==2)
return 1;
int c = 1;
for(int i=3;i<N;i+=2)
{
if(Ciur[i])
continue;
c++;
for(int j=i+i+i;j<N;j+=i+i)
Ciur[j]=true;
}
return c;
}
int main()
{
freopen("ciur.in","r",stdin);
freopen("ciur.out","w",stdout);
int N;
scanf("%d",&N);
int c = Solve(N);
printf("%d\n",c);
return 0;
}