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

int  prim(int n)
{
    int *a;int nr=0;
    a=(int *)calloc(n+1,sizeof(int));
    int i,j;
    for(i=2;i<=n;i++)
    {
        if(a[i]==0)
        {
            nr++;
            for(j=i+i;j<=n;j=j+i)
                a[j]=1;
        }
    }
    return nr;
}

int main()
{
    FILE * f = fopen("ciur.in","r");
    FILE * g = fopen("ciur.out","w");
    int n;
    fscanf(f,"%d",&n);
    fprintf(g,"%d",prim(n));

    return 0;
}