#include<stdio.h>
int eratos(int n)
{int v[n+1],i=0,j=0,t=0;
for(i=2;i<=n;i++)
v[i]=0;
for(i=2;i<=n;i++)
  {if(v[i]==0)
     { 
       t++;
       for(j=i*i;j<=n;j+=i)
       v[j]=1;}
       }
return t;
}

int main()
{FILE *f,*g;
f=fopen("ciur.in","r");
g=fopen("ciur.out","w");
int n;
fscanf(f,"%d",&n);
fprintf(g,"%d",eratos(n));
fclose(f);
fclose(g);
return 0;
}