#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#pragma warning(disable : 4996)
int check_number(int i);
int main()
{
int number, result=99,i,check_r;
scanf("%d", &number);

for (i = 100; i <= number; i++) {
if (number == 1000) number -= 1;
check_r = check_number(i);
result += check_r;
}
printf("%d\n", result);
return 0;

}
int check_number(int i) {
int a[3],j, num1, num2;
for (j = 0; j < 3; j++) {
a[j] = i / (int)pow(10,2-j);
i = i - a[j] * pow(10, 2 - j);
}
num1 = a[0] - a[1];
num2 = a[1] - a[2];
if (num1 == num2) return 1;
else return 0;

}