#include <iostream>
#include <stdio.h>
#define mx 50000005
using namespace std;
bool c[mx];
int main()
{
    freopen("primcolor.in", "r", stdin);
    freopen("primcolor.out", "w", stdout);
    int n,k=0;
    scanf("%d", &n);
    c[0]=1;
    for(int i=2; i*i<=n; ++i)
        if(c[i]==0)
        for(int j=i*i; j<=n; j=j+i)
        c[j]=1;
    for(int i=n/2+1; i<=n; ++i)
        if(c[i]==0)++k;
        if(n<3) printf("%d", n);
        else
    printf("%d", k+2);

    return 0;
}