#include <stdio.h>
#include <stdlib.h>

int main()
{
    FILE *f,*g;
    f=fopen("ciur.in","rt");
    g=fopen("ciur.out","wt");
    int N,i,j,v[2000000],nr=0;
    fscanf(f,"%d",&N);
    for(i=1; i<=N; i++)
        v[i]=1;
    for(i=2; i<=sqrt(N); i++)
    {
        if (v[i]==1)
            for (j=i; j<=N/i; j++)
                v[i*j]=0;
    }
    for (i=2; i<=N; i++)
        if (v[i])
            nr++;
    fprintf(g,"%d",nr);
    fclose(f);
    fclose(g);
    return 0;
}