#include <stdio.h>

int main(void) {
    printf("number of slices?\n");
    int slices;
    if ((scanf("%d", &slices) != 1) || (slices <= 0)) {
        printf("not a positive integer\n");
        return 1;
    } 
    double sum = 0.0;
    double width = 1.0 / slices;
    double tmp_x;
    for (int i = 0; i < slices; ++i) {
        tmp_x = (i+0.5)*width;
        sum += 4.0 / (1.0 + tmp_x * tmp_x);
    }
    double pi = sum * width; 
    printf("slices = %d\n", slices);
    printf("estimated pi = %f\n", pi);
    return 0;
}