#include<stdio.h>
using namespace std;
FILE *cin=fopen("ciur.in","r"), *cout=fopen("ciur.out","w");
int n,i,x,nr,j,prim[2000001];
int main()
{
    fscanf(cin,"%d",&n);
    for(i=2;i<=n;i++)
        prim[i]=1;
    for(i=2;i<=n;i++)
        if(prim[i]==1)
        {
            nr++;
            for(j=i+i;j<=n;j+=i)
            prim[j]=0;
        }
    fprintf(cout,"%d",nr);
}