#include<stdio.h>
#define nmax 2000005
int d, n, j, rez, i;
bool npr[nmax];

void ciur()
{

    for(d=2;d*d<=n;d++)
        if (!npr[d])
            for (j=2;j*d<=n;j++)
                npr[j*d]=1;
}

int main()
{
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%ld",&n);
    ciur();
    for (i=2;i<=n;i++)
        rez+=(1-npr[i]);
    printf("%ld",rez);
    return 0;
}