#include <cstdio>
#include <cmath>

const int c=2000000;
bool p[2000000];

void tabelprim()
{   int i,j,x;
    x=sqrt(c);
    p[1]=true;i=1;
    while(i<=x){
        do {i++;}while(p[i]==1);
        j=i*i;
        while(j<=c){p[j]=true;j+=i;};};
}

int main()
{   int i,n,x=0;
    tabelprim();
    freopen("ciur.in","r",stdin);
    freopen("ciur.out","w",stdout);
    scanf("%d",&n);
    for(i=2;i<=n;i++)if(!p[i])x++;
    printf("%d",x);
}