#include<stdio.h>
#include<math.h>
int main(){
    float radius;
    printf("Enter the radius of the circle:");
    scanf("%f",&radius);
    if(radius<0||radius>50){
        printf("Invalid input\n");
    }else{
        float area = M_P|*radius*radius;
        printf("%2f\n",area);
    }
    return 0;
}