#include<stdio.h>
#include<math.h>
long int k,i,j,n;
char v[2000001];
int main()
{
    FILE *f=fopen("ciur.in","r"), *g=fopen("ciur.out","w");
    fscanf(f,"%ld",&n);
    for (i=1;i<=n;++i) v[i]='0';
    for (i=2;i<=n;++i)
        if (v[i]=='0')
           {
           k++;
           for(j=i;j<=n;j+=i)
			     v[j]='1';
           }
    fprintf(g,"%ld",k);
return 0;
}