#include <stdio.h>
char prim[2000000];
int Eratosthenes(int n)
{int nr=0,i,j;
for (i=2;i<=n;++i)
if(prim[i]==0)
{++nr;
for(j=i+i;j<=n;j+= i)
prim[j]=1;
}
return nr;
}


int main()
{int n,nr=0,i,j;
FILE *fin,*fout;  
fin=fopen("ciur.in","r");
fout=fopen("ciur.out","w");
fscanf(fin,"%d",&n);
fprintf(fout,"%d",Eratosthenes(n));
return 0;
}