题解 | #自守数#

#define _CRT_SECURE_NO_WARNINGS
#include <stdio.h>
#include <math.h>
int main() {
    int n;
    scanf("%d", &n);
    int count = 0, count2 = 1;
    for (int i = 1; i <= n; i++) {
        int num = i;
        while (num) {
            num /= 10;
            count++;
        }
        int mod = (int)(i * i) % ((int)pow(10, count));
        if (mod == i) {
            count2++;
        }
        count = 0;
    }
    printf("%d", count2);
    return 0;
}