#include<stdio.h>
char v[2000001];


int main()
{FILE *f,*g;
f=fopen("ciur.in","r");
g=fopen("ciur.out","w");
long n=0,i=0,j=0,c=0;
fscanf(f,"%ld",&n);
for(i=2;i<=n;i++)
if(v[i]==0)
{c++;for(j=i*i;j<=n;j+=i)
     v[j]=1;}
     
fprintf(g,"%ld",c);
fclose(f);
fclose(g);
return 0;
}