#include <stdio.h>
#include <stdlib.h>
#define MAX 2000000
int v[MAX];
int main()
{
    int i,j,nr=0,n;
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=2;i<=n;i++)
        if(!v[i])
            for(j=i+i;j<=n;j=j+i)
                v[j]=1;
    for(i=2;i<=n;i++)
        if(v[i]==0)
            nr++;
    printf("%d",nr);
    return 0;
}