#include<stdio.h>

const int maxn = 2000005;
 
bool ciur[maxn];
int n, cnt;
 
int main()
{
	FILE* f1,*f2;
	f1=fopen("ciur.in","r");
	f2=fopen("ciur.out","w");
	fscanf(f1,"%d",&n);

    ciur[1] = 1;
    for(int i = 2 ; i <= n;  i++) 
	{
        if(ciur[i] == 0)
		{
            cnt ++;
            for(int j = i + i ; j <= n ; j = j + i)
                ciur[j] = 1;
        }
    }
    fprintf(f2,"%d",cnt);
    return 0;
}