#include<cstdio>
using namespace std;
bool prim[2000001];
int n,nr;
int ciur()
{
    prim[1]=1;
    prim[0]=1;
    for(int i=2; i<=n/2; i++)
    {
        if(i>1414||prim[i]==1) continue;
        for(int j=i*i; j<=n; j+=i) prim[j]=1;
    }
    for(int i=1; i<=n; i++) if(!prim[i]) nr++;
}
int main()
{
    FILE *fin,*fout;
    fin=fopen("ciur.in","r");
    fout=fopen("ciur.out","w");
    fscanf(fin,"%d",&n);
    ciur();
    fprintf(fout,"%d",nr);
}