#include <iostream>
#include<cstdio>
#define NMAX 10000
using namespace std;
int ciur[NMAX],n,i,j,nr;
int main()
{
    FILE *fin=fopen("ciur.in", "r");
    FILE *fout=fopen("ciur.out", "w");
    fscanf (fin,"%d", &n);
    for(i=2;i<=n;i++)
        ciur[i]=1;
    for(i=2;i<=n;i++)
    {
        if(ciur[i])
        {
            nr++;
            for(j=2;j*i<=n;j++)
                ciur[i*j]=0;
        }
    }
    fprintf(fout,"%d",nr);
    fclose(fout);
    return 0;

}