#include<stdio.h>

bool c[2000001];

using namespace std;

int main()
{
    FILE *in,*out;
    in=fopen("ciur.in","r");
    out=fopen("ciur.out","w");
    int i,j,n,nr=0;
    fscanf(in,"%d",&n);
    for(i=2; i*i<=n; i++)
    {
        if(!c[i])
            for(j=i*i; j<=n; j+=i)
                c[j]=true;
    }
    for(i=2; i<=n; i++)
    {
        if(!c[i])
            nr++;
    }
    fprintf(out,"%d",nr);
    return 0;
}