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

    printf("%d",nr);
    return 0;
}