#include <stdio.h>
 
int main(void) {
    int num, i, isPrime = 1;  // isPrimeは素数判定用フラグ
 
    printf("整数を入力してください: ");
    scanf("%d", &num);
 
    if (num <= 1) {
        printf("1以上の整数を入力してください。\n");
        return 0;
    }
 
    for (i = 2; i * i <= num; i++) {
        if (num % i == 0) {
            isPrime = 0;  // 割り切れたら素数ではない
            break;
        }
    }
 
    if (isPrime) {
        printf("%d は素数です。\n", num);
    } else {
        printf("%d は素数ではありません。\n", num);
    }
 
    return 0;
}
 

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