#include <stdio.h>
 
int main(void)
{
    int a;
    int i;
    int x= 1;  // 素数と仮定しておく
 
    printf("正の整数aを入力してください: ");
    scanf("%d", &a);
 
    if (a <= 1) {
        printf("%d は素数ではありません\n", a);
        return 0;
    }
 
    for (i = 2; i * i <= a; i++) {
        if (a % i == 0) {
            x= 0;  
            break;
        }
    }
 
    if (x)
        printf("%d は素数です\n", a);
    else
        printf("%d は素数ではありません\n", a);
 
    return 0;
}

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