#define _USE_MATH_DEFINES
#define M_EPS (double)1e-20

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <stdbool.h>

double foo(double x) {
    return sqrt(sin(x));
}

double integrate(double a, double b, int n) {
    double h = (b - a) / n;
    double res = 0;
    for (int i = 0; i <= n; i++) {
        if (i == 0 || i == n) {
            res += foo(a + i * h) / 2; 
        } else {
            res += foo(a + i * h);
        }
    }
    return h * res;
}

int main(void) {
    double a, b, epsilon;
    scanf("%lf %lf %lf", &a, &b, &epsilon);

    if (a > b) {
        printf("a > b");
        return 0;
    } else if (fabs(a - b) < M_EPS) {
        printf("0");
        return 0;
    } else if (sin(a) < 0 || sin(b) < 0 || b - a > M_PI) {
        printf("sin(x) < 0");
        return 0;
    }

    double sPrev = integrate(a, b, 1), sCur = 0;
    int n = 2;

    while (true) {
        sCur = integrate(a, b, n);
        if (fabs(sPrev - sCur) < epsilon) {
            break;
        }
        sPrev = sCur;
        n++;
    }
    printf("%.16f", sCur);
    return 0;
}