#include<cstdio>
#define CLOSE fclose(in); fclose(out); return 0;
using namespace std;
FILE *in,*out;

const int LIM = 2000100;
int v[LIM+10];

void ciur(){
    for(register int i = 2; i<=LIM; ++i)
        if(!v[i])
            for(register long long j = (long long)i*i; j<=LIM; j+=i)
                v[j]=1;
}

inline int negatie (int a){
    return a==0 ? 1 : 0;
}

void sume(){
    for(register int i =2; i<=LIM; ++i)
        v[i]=v[i-1]+negatie(v[i]);
}

int main(){
    in=fopen("ciur.in","r");
    out=fopen("ciur.out","w");

    ciur();
    sume();

    int X;
    fscanf(in,"%d",&X);
    fprintf(out,"%d\n",v[X]);
    CLOSE
}