#include<stdio.h>
#define max 2000000
FILE *in=fopen("ciur.in","rt");
FILE *out=fopen("ciur.out","wt");
int j,i,n,prim[max],cont;

int main()
{
    fscanf(in,"%d",&n);
    for(i=2;i<=n;i++)
    if(prim[i]==0)
    {
        for(j=i*2;j<=n;j+=i)
            prim[j]=1;
    }
    for(i=2;i<=n;i++)
        if(prim[i]==0)
            cont++;
    fprintf(out,"%d",cont);
    return 0;
}