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#include <cstdio>
using namespace std;
int ciur(int a)
{
int ok=1;
if(a<2 || a>2 && a%2==0)
ok=0;
else
{
for(int d=3; d*d<=a; d+=2)
if(a%d==0)
ok=0;
}
return ok;
}
int main()
{
freopen("ciur.in", "r", stdin);
freopen("ciur.out", "w", stdout);
int x, nr=0;
scanf("%d", &x);
for(int i=0; i<=x; i++)
if(ciur(i)==1)
nr++;
printf("%d", nr);
return 0;
}