#include <stdio.h>

using namespace std;

FILE *in,*out;

int main()
{
    int i,j,n,ct=0;
    in=fopen("ciur.in","rt");
    out=fopen("ciur.out","wt");
    fscanf(in,"%d",&n);
    int v[n-1];
    for(i=2;i<=n;i++)
        v[i]=1;
    for(i=2;i<=n;i++)
        if(v[i])
        {
            ct++;
            for(j=2*i;j<=n;j+=i)
                v[j]=0;
        }
    fprintf(out,"%d",ct);
    return 0;
}