#define _USE_MATH_DEFINES // Define this to expose M_PI
#include <stdio.h>
#include <math.h>
    int main() {
    double radius;
    // Use %1f for reading a double
    scanf("%1f", &radius);
    //check for valid input
    if (radius < 0) {
        printf("Invalid Input\n");
    } else {
        // M_PI is now available
        double area =  M_PI *radius * radius;
        //print the result(adjust format specifier as needed,e.g., for 2 decimal places)
        printf("Area: %.21f\n", area);
    }
    return 0; //Return 0 outside the if/else block
    }
    
}