#include<stdio.h>
char c[2000001];
int main()
{
    FILE *in,*out;
    in=fopen("ciur.in","r");
    out=fopen("ciur.out","w");
    int i,n,j,nr=0;
    fscanf(in,"%d",&n);
    for(i=2;i*i<=n;i++)
        if(!c[i])//c[i]==0
        for(j=i*i;j<=n;j+=i)
            c[j]=1;
    for(i=2;i<=n;i++)
        if(c[i]==0)
            nr++;
    fprintf(out,"%d",nr);
    return 0;

}