#include<stdio.h>

int n, i, j;
bool prim[2000002];

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

	

	fscanf(inputFile, "%d", &n);
	int cnt=0;
	for(i=2; i<=n; i++)
		prim[i]=true;
	for(i=2; i<=n; i++)
	{
		if(prim[i] == true)
		{
			cnt++;
			for(j=i+i; j<=n; j=j+i)
				prim[j]=false;
		}
	}
	fprintf(outputFile, "%d", cnt);

	return 0;
}