function main(lines) {
    const input = lines.split(' ').map(Number)
    const x1 = input[0]
    const y1 = input[1]
    const x2 = input[2]
    const y2 = input[3]

    console.log(Math.sqrt(Math.pow(abs(x1-x2),2) + Math.pow(abs(y1-y2),2)).toFixed(4))
    
    function abs(val){
        return val < 0 ? -val : val;
    }
}

main(require('fs').readFileSync('/dev/stdin', 'utf8'));

