#include<stdio.h>
int main() { int i,j,nr,n;
bool c[2000005];
FILE *f,*g;
f=fopen("ciur.in","r");
g=fopen("ciur.out","w");
fscanf(f,"%d",&n);
if (n==2) fprintf(g,"0");
else
{
nr=0;
for (i=2;i<=n;i++) if (c[i]==false) for (j=i+i;j<=n;j+=i) c[j]=true;
for (i=2;i<=n;i++) if (!c[i]) nr++;
 
fprintf(g,"%d",nr);
}
fclose(f);
fclose(g);
return 0;
}