#include<stdio.h>
int v[2000000],i,j,n,k;
int main(){
FILE *f=fopen("ciur.in","r");
FILE *g=fopen("ciur.out","w");
fscanf(f,"%d",&n);
for(i=2;i<=n;i++)
        {if(!v[i])
                {k++;
                for(j=i*i;j<=n;j+=i)
                        v[j]=1;
                 }
         }
fprintf(g,"%d",k);
fclose(g);
fclose(f);
return 0;}